text: .17 anton 5: @settitle Gforth Manual 1.4 anton 6: @comment @setchapternewpage odd 1.1 anton 7: @comment %**end of header (This is for running Texinfo on a region.) 8: 9: @ifinfo 1.17 anton 10: This file documents Gforth 0.1 1.1 anton 11: 1.21 anton 12: Copyright @copyright{} 1995 Free Software Foundation, Inc. 1.1 anton: 1.24 anton 39: @finalout 1.1 anton 40: @titlepage 41: @sp 10 1.17 anton 42: @center @titlefont{Gforth Manual} 1.1 anton 43: @sp 2 1.17 anton 44: @center for version 0.21 anton 54: Copyright @copyright{} 1995 Free Software Foundation, Inc. 1.1 anton 1.17 anton 79: Gforth is a free implementation of ANS Forth available on many 1.21 anton 80: personal machines. This manual corresponds to version 0 100: @unnumbered GNU GENERAL PUBLIC LICENSE 101: @center Version 2, June 1991 102: 103: @display 104: Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. 105: 675 Mass Ave, Cambridge, MA 02139, USA 106: 107: Everyone is permitted to copy and distribute verbatim copies 108: of this license document, but changing it is not allowed. 109: @end display 110: 111: @unnumberedsec Preamble 112: 113: The licenses for most software are designed to take away your 114: freedom to share and change it. By contrast, the GNU General Public 115: License is intended to guarantee your freedom to share and change free 116: software---to make sure the software is free for all its users. This 117: General Public License applies to most of the Free Software 118: Foundation's software and to any other program whose authors commit to 119: using it. (Some other Free Software Foundation software is covered by 120: the GNU Library General Public License instead.) You can apply it to 121: your programs, too. 122: 123: When we speak of free software, we are referring to freedom, not 124: price. Our General Public Licenses are designed to make sure that you 125: have the freedom to distribute copies of free software (and charge for 126: this service if you wish), that you receive source code or can get it 127: if you want it, that you can change the software or use pieces of it 128: in new free programs; and that you know you can do these things. 129: 130: To protect your rights, we need to make restrictions that forbid 131: anyone to deny you these rights or to ask you to surrender the rights. 132: These restrictions translate to certain responsibilities for you if you 133: distribute copies of the software, or if you modify it. 134: 135: For example, if you distribute copies of such a program, whether 136: gratis or for a fee, you must give the recipients all the rights that 137: you have. You must make sure that they, too, receive or can get the 138: source code. And you must show them these terms so they know their 139: rights. 140: 141: We protect your rights with two steps: (1) copyright the software, and 142: (2) offer you this license which gives you legal permission to copy, 143: distribute and/or modify the software. 144: 145: Also, for each author's protection and ours, we want to make certain 146: that everyone understands that there is no warranty for this free 147: software. If the software is modified by someone else and passed on, we 148: want its recipients to know that what they have is not the original, so 149: that any problems introduced by others will not reflect on the original 150: authors' reputations. 151: 152: Finally, any free program is threatened constantly by software 153: patents. We wish to avoid the danger that redistributors of a free 154: program will individually obtain patent licenses, in effect making the 155: program proprietary. To prevent this, we have made it clear that any 156: patent must be licensed for everyone's free use or not licensed at all. 157: 158: The precise terms and conditions for copying, distribution and 159: modification follow. 160: 161: @iftex 162: @unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 163: @end iftex 164: @ifinfo 165: @center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 166: @end ifinfo 167: 168: @enumerate 0 169: @item 170: This License applies to any program or other work which contains 171: a notice placed by the copyright holder saying it may be distributed 172: under the terms of this General Public License. The ``Program'', below, 173: refers to any such program or work, and a ``work based on the Program'' 174: means either the Program or any derivative work under copyright law: 175: that is to say, a work containing the Program or a portion of it, 176: either verbatim or with modifications and/or translated into another 177: language. (Hereinafter, translation is included without limitation in 178: the term ``modification''.) Each licensee is addressed as ``you''. 179: 180: Activities other than copying, distribution and modification are not 181: covered by this License; they are outside its scope. The act of 182: running the Program is not restricted, and the output from the Program 183: is covered only if its contents constitute a work based on the 184: Program (independent of having been made by running the Program). 185: Whether that is true depends on what the Program does. 186: 187: @item 188: You may copy and distribute verbatim copies of the Program's 189: source code as you receive it, in any medium, provided that you 190: conspicuously and appropriately publish on each copy an appropriate 191: copyright notice and disclaimer of warranty; keep intact all the 192: notices that refer to this License and to the absence of any warranty; 193: and give any other recipients of the Program a copy of this License 194: along with the Program. 195: 196: You may charge a fee for the physical act of transferring a copy, and 197: you may at your option offer warranty protection in exchange for a fee. 198: 199: @item 200: You may modify your copy or copies of the Program or any portion 201: of it, thus forming a work based on the Program, and copy and 202: distribute such modifications or work under the terms of Section 1 203: above, provided that you also meet all of these conditions: 204: 205: @enumerate a 206: @item 207: You must cause the modified files to carry prominent notices 208: stating that you changed the files and the date of any change. 209: 210: @item 211: You must cause any work that you distribute or publish, that in 212: whole or in part contains or is derived from the Program or any 213: part thereof, to be licensed as a whole at no charge to all third 214: parties under the terms of this License. 215: 216: @item 217: If the modified program normally reads commands interactively 218: when run, you must cause it, when started running for such 219: interactive use in the most ordinary way, to print or display an 220: announcement including an appropriate copyright notice and a 221: notice that there is no warranty (or else, saying that you provide 222: a warranty) and that users may redistribute the program under 223: these conditions, and telling the user how to view a copy of this 224: License. (Exception: if the Program itself is interactive but 225: does not normally print such an announcement, your work based on 226: the Program is not required to print an announcement.) 227: @end enumerate 228: 229: These requirements apply to the modified work as a whole. If 230: identifiable sections of that work are not derived from the Program, 231: and can be reasonably considered independent and separate works in 232: themselves, then this License, and its terms, do not apply to those 233: sections when you distribute them as separate works. But when you 234: distribute the same sections as part of a whole which is a work based 235: on the Program, the distribution of the whole must be on the terms of 236: this License, whose permissions for other licensees extend to the 237: entire whole, and thus to each and every part regardless of who wrote it. 238: 239: Thus, it is not the intent of this section to claim rights or contest 240: your rights to work written entirely by you; rather, the intent is to 241: exercise the right to control the distribution of derivative or 242: collective works based on the Program. 243: 244: In addition, mere aggregation of another work not based on the Program 245: with the Program (or with a work based on the Program) on a volume of 246: a storage or distribution medium does not bring the other work under 247: the scope of this License. 248: 249: @item 250: You may copy and distribute the Program (or a work based on it, 251: under Section 2) in object code or executable form under the terms of 252: Sections 1 and 2 above provided that you also do one of the following: 253: 254: @enumerate a 255: @item 256: Accompany it with the complete corresponding machine-readable 257: source code, which must be distributed under the terms of Sections 258: 1 and 2 above on a medium customarily used for software interchange; or, 259: 260: @item 261: Accompany it with a written offer, valid for at least three 262: years, to give any third party, for a charge no more than your 263: cost of physically performing source distribution, a complete 264: machine-readable copy of the corresponding source code, to be 265: distributed under the terms of Sections 1 and 2 above on a medium 266: customarily used for software interchange; or, 267: 268: @item 269: Accompany it with the information you received as to the offer 270: to distribute corresponding source code. (This alternative is 271: allowed only for noncommercial distribution and only if you 272: received the program in object code or executable form with such 273: an offer, in accord with Subsection b above.) 274: @end enumerate 275: 276: The source code for a work means the preferred form of the work for 277: making modifications to it. For an executable work, complete source 278: code means all the source code for all modules it contains, plus any 279: associated interface definition files, plus the scripts used to 280: control compilation and installation of the executable. However, as a 281: special exception, the source code distributed need not include 282: anything that is normally distributed (in either source or binary 283: form) with the major components (compiler, kernel, and so on) of the 284: operating system on which the executable runs, unless that component 285: itself accompanies the executable. 286: 287: If distribution of executable or object code is made by offering 288: access to copy from a designated place, then offering equivalent 289: access to copy the source code from the same place counts as 290: distribution of the source code, even though third parties are not 291: compelled to copy the source along with the object code. 292: 293: @item 294: You may not copy, modify, sublicense, or distribute the Program 295: except as expressly provided under this License. Any attempt 296: otherwise to copy, modify, sublicense or distribute the Program is 297: void, and will automatically terminate your rights under this License. 298: However, parties who have received copies, or rights, from you under 299: this License will not have their licenses terminated so long as such 300: parties remain in full compliance. 301: 302: @item 303: You are not required to accept this License, since you have not 304: signed it. However, nothing else grants you permission to modify or 305: distribute the Program or its derivative works. These actions are 306: prohibited by law if you do not accept this License. Therefore, by 307: modifying or distributing the Program (or any work based on the 308: Program), you indicate your acceptance of this License to do so, and 309: all its terms and conditions for copying, distributing or modifying 310: the Program or works based on it. 311: 312: @item 313: Each time you redistribute the Program (or any work based on the 314: Program), the recipient automatically receives a license from the 315: original licensor to copy, distribute or modify the Program subject to 316: these terms and conditions. You may not impose any further 317: restrictions on the recipients' exercise of the rights granted herein. 318: You are not responsible for enforcing compliance by third parties to 319: this License. 320: 321: @item 322: If, as a consequence of a court judgment or allegation of patent 323: infringement or for any other reason (not limited to patent issues), 324: conditions are imposed on you (whether by court order, agreement or 325: otherwise) that contradict the conditions of this License, they do not 326: excuse you from the conditions of this License. If you cannot 327: distribute so as to satisfy simultaneously your obligations under this 328: License and any other pertinent obligations, then as a consequence you 329: may not distribute the Program at all. For example, if a patent 330: license would not permit royalty-free redistribution of the Program by 331: all those who receive copies directly or indirectly through you, then 332: the only way you could satisfy both it and this License would be to 333: refrain entirely from distribution of the Program. 334: 335: If any portion of this section is held invalid or unenforceable under 336: any particular circumstance, the balance of the section is intended to 337: apply and the section as a whole is intended to apply in other 338: circumstances. 339: 340: It is not the purpose of this section to induce you to infringe any 341: patents or other property right claims or to contest validity of any 342: such claims; this section has the sole purpose of protecting the 343: integrity of the free software distribution system, which is 344: implemented by public license practices. Many people have made 345: generous contributions to the wide range of software distributed 346: through that system in reliance on consistent application of that 347: system; it is up to the author/donor to decide if he or she is willing 348: to distribute software through any other system and a licensee cannot 349: impose that choice. 350: 351: This section is intended to make thoroughly clear what is believed to 352: be a consequence of the rest of this License. 353: 354: @item 355: If the distribution and/or use of the Program is restricted in 356: certain countries either by patents or by copyrighted interfaces, the 357: original copyright holder who places the Program under this License 358: may add an explicit geographical distribution limitation excluding 359: those countries, so that distribution is permitted only in or among 360: countries not thus excluded. In such case, this License incorporates 361: the limitation as if written in the body of this License. 362: 363: @item 364: The Free Software Foundation may publish revised and/or new versions 365: of the General Public License from time to time. Such new versions will 366: be similar in spirit to the present version, but may differ in detail to 367: address new problems or concerns. 368: 369: Each version is given a distinguishing version number. If the Program 370: specifies a version number of this License which applies to it and ``any 371: later version'', you have the option of following the terms and conditions 372: either of that version or of any later version published by the Free 373: Software Foundation. If the Program does not specify a version number of 374: this License, you may choose any version ever published by the Free Software 375: Foundation. 376: 377: @item 378: If you wish to incorporate parts of the Program into other free 379: programs whose distribution conditions are different, write to the author 380: to ask for permission. For software which is copyrighted by the Free 381: Software Foundation, write to the Free Software Foundation; we sometimes 382: make exceptions for this. Our decision will be guided by the two goals 383: of preserving the free status of all derivatives of our free software and 384: of promoting the sharing and reuse of software generally. 385: 386: @iftex 387: @heading NO WARRANTY 388: @end iftex 389: @ifinfo 390: @center NO WARRANTY 391: @end ifinfo 392: 393: @item 394: BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY 395: FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN 396: OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES 397: PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED 398: OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 399: MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS 400: TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE 401: PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, 402: REPAIR OR CORRECTION. 403: 404: @item 405: IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 406: WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR 407: REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, 408: INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING 409: OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED 410: TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY 411: YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER 412: PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE 413: POSSIBILITY OF SUCH DAMAGES. 414: @end enumerate 415: 416: @iftex 417: @heading END OF TERMS AND CONDITIONS 418: @end iftex 419: @ifinfo 420: @center END OF TERMS AND CONDITIONS 421: @end ifinfo 422: 423: @page 424: @unnumberedsec How to Apply These Terms to Your New Programs 425: 426: If you develop a new program, and you want it to be of the greatest 427: possible use to the public, the best way to achieve this is to make it 428: free software which everyone can redistribute and change under these terms. 429: 430: To do so, attach the following notices to the program. It is safest 431: to attach them to the start of each source file to most effectively 432: convey the exclusion of warranty; and each file should have at least 433: the ``copyright'' line and a pointer to where the full notice is found. 434: 435: @smallexample 436: @var{one line to give the program's name and a brief idea of what it does.} 437: Copyright (C) 19@var{yy} @var{name of author} 438: 439: This program is free software; you can redistribute it and/or modify 440: it under the terms of the GNU General Public License as published by 441: the Free Software Foundation; either version 2 of the License, or 442: (at your option) any later version. 443: 444: This program is distributed in the hope that it will be useful, 445: but WITHOUT ANY WARRANTY; without even the implied warranty of 446: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 447: GNU General Public License for more details. 448: 449: You should have received a copy of the GNU General Public License 450: along with this program; if not, write to the Free Software 451: Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 452: @end smallexample 453: 454: Also add information on how to contact you by electronic and paper mail. 455: 456: If the program is interactive, make it output a short notice like this 457: when it starts in an interactive mode: 458: 459: @smallexample 460: Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author} 461: Gnomovision comes with ABSOLUTELY NO WARRANTY; for details 462: type `show w'. 463: This is free software, and you are welcome to redistribute it 464: under certain conditions; type `show c' for details. 465: @end smallexample 466: 467: The hypothetical commands @samp{show w} and @samp{show c} should show 468: the appropriate parts of the General Public License. Of course, the 469: commands you use may be called something other than @samp{show w} and 470: @samp{show c}; they could even be mouse-clicks or menu items---whatever 471: suits your program. 472: 473: You should also get your employer (if you work as a programmer) or your 474: school, if any, to sign a ``copyright disclaimer'' for the program, if 475: necessary. Here is a sample; alter the names: 476: 477: @smallexample 478: Yoyodyne, Inc., hereby disclaims all copyright interest in the program 479: `Gnomovision' (which makes passes at compilers) written by James Hacker. 480: 481: @var{signature of Ty Coon}, 1 April 1989 482: Ty Coon, President of Vice 483: @end smallexample 484: 485: This General Public License does not permit incorporating your program into 486: proprietary programs. If your program is a subroutine library, you may 487: consider it more useful to permit linking proprietary applications with the 488: library. If this is what you want to do, use the GNU Library General 489: Public License instead of this License. 511: @item 512: It should be a model, i.e. it should define all the 513: implementation-dependent things. 514: @item 515: It should become standard, i.e. widely accepted and used. This goal 516: is the most difficult one. 517: @end itemize 518: 1.17 anton 519: To achieve these goals Gforth should be 1.1 anton 520: @itemize @bullet 521: @item 522: Similar to previous models (fig-Forth, F83) 523: @item 524: Powerful. It should provide for all the things that are considered 525: necessary today and even some that are not yet considered necessary. 526: @item 527: Efficient. It should not get the reputation of being exceptionally 528: slow. 529: @item 530: Free. 531: @item 532: Available on many machines/easy to port. 533: @end itemize 534: 538: change. It certainly has not yet become a de facto standard. It has some 539: similarities and some differences to previous models. It has some 540: powerful features, but not yet everything that we envisioned. We 541: certainly have achieved our execution speed goals (@pxref{Performance}). 542: It is free and available on many machines. 553: write ANS Forth programs. It is available in printed form from the 554: National Standards Institute Sales Department (Tel.: USA (212) 642-4900; 555: Fax.: USA (212) 302-1286) as document @cite{X3.215-1994} for about $200. You 556: can also get it from Global Engineering Documents (Tel.: USA (800) 557: 854-7179; Fax.: (303) 843-9880) for about $300. 558: 559: @cite{dpANS6}, the last draft of the standard, which was then submitted to ANSI 560: for publication is available electronically and for free in some MS Word 561: format, and it has been converted to HTML. Some pointers to these 562: versions can be found through 1.24 anton 563: @*@file{}. 1.1 anton 564: 1.21 anton 565: @cite{Forth: The new model} by Jack Woehr (Prentice-Hall, 1993) is an 1.1 anton 566: introductory book based on a draft version of the standard. It does not 567: cover the whole standard. It also contains interesting background 568: information (Jack Woehr was in the ANS Forth Technical Committe). It is 569: not appropriate for complete newbies, but programmers experienced in 570: other languages should find it ok. 571: 572: @node Invocation, Words, Other Books, Top 573: @chapter Invocation 574: 575: You will usually just say @code{gforth}. In many other cases the default 1.17 anton 576: Gforth image will be invoked like this: 1.1 anton 577: 578: @example 579: gforth [files] [-e forth-code] 580: @end example 581: 582: executing the contents of the files and the Forth code in the order they 583: are given. 584: 585: In general, the command line looks like this: 586: 587: @example 588: gforth [initialization options] [image-specific options] 589: @end example 590: 591: The initialization options must come before the rest of the command 592: line. They are: 593: 594: @table @code 595: @item --image-file @var{file} 602: Uses @var{path} for searching the image file and Forth source code 603: files instead of the default in the environment variable 604: @code{GFORTHPATH} or the path specified at installation time (typically 605: @file{/usr/local/lib/gforth:.}). A path is given as a @code{:}-separated 606: list. 607: 608: @item --dictionary-size @var{size} 609: @item -m @var{size} 610: Allocate @var{size} space for the Forth dictionary space instead of 611: using the default specified in the image (typically 256K). The 612: @var{size} specification consists of an integer and a unit (e.g., 613: @code{4M}). The unit can be one of @code{b} (bytes), @code{e} (element 614: size, in this case Cells), @code{k} (kilobytes), and @code{M} 615: (Megabytes). If no unit is specified, @code{e} is used. 616: 617: @item --data-stack-size @var{size} 618: @item -d @var{size} 619: Allocate @var{size} space for the data stack instead of using the 620: default specified in the image (typically 16K). 621: 622: @item --return-stack-size @var{size} 623: @item -r @var{size} 624: Allocate @var{size} space for the return stack instead of using the 625: default specified in the image (typically 16K). 626: 627: @item --fp-stack-size @var{size} 628: @item -f @var{size} 629: Allocate @var{size} space for the floating point stack instead of 630: using the default specified in the image (typically 16K). In this case 631: the unit specifier @code{e} refers to floating point numbers. 632: 633: @item --locals-stack-size @var{size} 634: @item -l @var{size} 635: Allocate @var{size} space for the locals stack instead of using the 636: default specified in the image (typically 16K). 637: 638: @end table 639: 640: As explained above, the image-specific command-line arguments for the 641: default image @file{gforth.fi} consist of a sequence of filenames and 642: @code{-e @var{forth-code}} options that are interpreted in the seqence 643: in which they are given. The @code{-e @var{forth-code}} or 644: @code{--evaluate @var{forth-code}} option evaluates the forth 645: code. This option takes only one argument; if you want to evaluate more 646: Forth words, you have to quote them or use several @code{-e}s. To exit 647: after processing the command line (instead of entering interactive mode) 648: append @code{-e bye} to the command line. 649: 1.22 anton 650: If you have several versions of Gforth installed, @code{gforth} will 651: invoke the version that was installed last. @code{gforth-@var{version}} 652: invokes a specific version. You may want to use the option 653: @code{--path}, if your environment contains the variable 654: @code{GFORTHPATH}. 655: 1.1 anton 656: Not yet implemented: 657: On startup the system first executes the system initialization file 658: (unless the option @code{--no-init-file} is given; note that the system 659: resulting from using this option may not be ANS Forth conformant). Then 660: the user initialization file @file{.gforth.fs} is executed, unless the 661: option @code{--no-rc} is given; this file is first searched in @file{.}, 662: then in @file{~}, then in the normal path (see above). 663: 682: @end menu 683: 684: @node Notation, Arithmetic, Words, Words 685: @section Notation 686: 687: The Forth words are described in this section in the glossary notation 688: that has become a de-facto standard for Forth texts, i.e. 689: 699: 700: @item Stack effect 701: The stack effect is written in the notation @code{@var{before} -- 702: @var{after}}, where @var{before} and @var{after} describe the top of 703: stack entries before and after the execution of the word. The rest of 704: the stack is not touched by the word. The top of stack is rightmost, 1.17 anton 705: i.e., a stack sequence is written as it is typed in. Note that Gforth 1.1 anton 706: uses a separate floating point stack, but a unified stack 707: notation. Also, return stack effects are not shown in @var{stack 708: effect}, but in @var{Description}. The name of a stack item describes 709: the type and/or the function of the item. See below for a discussion of 710: the types. 711: 1.19 anton 712: All words have two stack effects: A compile-time stack effect and a 713: run-time stack effect. The compile-time stack-effect of most words is 714: @var{ -- }. If the compile-time stack-effect of a word deviates from 715: this standard behaviour, or the word does other unusual things at 716: compile time, both stack effects are shown; otherwise only the run-time 717: stack effect is shown. 718: 1.1 anton 719: @item pronunciation 720: How the word is pronounced 721: 722: @item wordset 723: The ANS Forth standard is divided into several wordsets. A standard 724: system need not support all of them. So, the fewer wordsets your program 725: uses the more portable it will be in theory. However, we suspect that 726: most ANS Forth systems on personal machines will feature all 727: wordsets. Words that are not defined in the ANS standard have 1.19 anton 728: @code{gforth} or @code{gforth-internal} as wordset. @code{gforth} 729: describes words that will work in future releases of Gforth; 730: @code{gforth-internal} words are more volatile. Environmental query 731: strings are also displayed like words; you can recognize them by the 732: @code{environment} in the wordset field. 740: 741: @table @code 742: @item f 743: Bool, i.e. @code{false} or @code{true}. 744: @item c 745: Char 746: @item w 747: Cell, can contain an integer or an address 748: @item n 749: signed integer 750: @item u 751: unsigned integer 752: @item d 753: double sized signed integer 754: @item ud 755: double sized unsigned integer 756: @item r 757: Float 758: @item a_ 759: Cell-aligned address 760: @item c_ 761: Char-aligned address (note that a Char is two bytes in Windows NT) 762: @item f_ 763: Float-aligned address 764: @item df_ 765: Address aligned for IEEE double precision float 766: @item sf_ 767: Address aligned for IEEE single precision float 768: @item xt 769: Execution token, same size as Cell 770: @item wid 771: Wordlist ID, same size as Cell 772: @item f83name 773: Pointer to a name structure 774: @end table 775: 1.4 anton 776: @node Arithmetic, Stack Manipulation, Notation, Words 1.1 anton 777: @section Arithmetic 778: Forth arithmetic is not checked, i.e., you will not hear about integer 779: overflow on addition or multiplication, you may hear about division by 780: zero if you are lucky. The operator is written after the operands, but 781: the operands are still in the original order. I.e., the infix @code{2-1} 782: corresponds to @code{2 1 -}. Forth offers a variety of division 783: operators. If you perform division with potentially negative operands, 784: you do not want to use @code{/} or @code{/mod} with its undefined 785: behaviour, but rather @code{fm/mod} or @code{sm/mod} (probably the 846: 847: The format of floating point numbers recognized by the outer (aka text) 848: interpreter is: a signed decimal number, possibly containing a decimal 849: point (@code{.}), followed by @code{E} or @code{e}, optionally followed 850: by a signed integer (the exponent). E.g., @code{1e} ist the same as 851: @code{+1.0e+1}. Note that a number without @code{e} 852: is not interpreted as floating-point number, but as double (if the 853: number contains a @code{.}) or single precision integer. Also, 854: conversions between string and floating point numbers always use base 855: 10, irrespective of the value of @code{BASE}. If @code{BASE} contains a 856: value greater then 14, the @code{E} may be interpreted as digit and the 857: number will be interpreted as integer, unless it has a signed exponent 858: (both @code{+} and @code{-} are allowed as signs). 1.4 anton 859: 860: Angles in floating point operations are given in radians (a full circle 1.17 anton 861: has 2 pi radians). Note, that Gforth has a separate floating point 1.4 anton 862: stack, but we use the unified notation. 863: 864: Floating point numbers have a number of unpleasant surprises for the 865: unwary (e.g., floating point addition is not associative) and even a few 866: for the wary. You should not use them unless you know what you are doing 867: or you don't care that the results you get are totally bogus. If you 868: want to learn about the problems of floating point numbers (and how to 1.11 anton 869: avoid them), you might start with @cite{David Goldberg, What Every 1.6 anton 870: Computer Scientist Should Know About Floating-Point Arithmetic, ACM 871: Computing Surveys 23(1):5@minus{}48, March 1991}. 1.4 anton 872: 873: doc-f+ 874: doc-f- 875: doc-f* 876: doc-f/ 877: doc-fnegate 878: doc-fabs 879: doc-fmax 880: doc-fmin 881: doc-floor 882: doc-fround 883: doc-f** 884: doc-fsqrt 885: doc-fexp 886: doc-fexpm1 887: doc-fln 888: doc-flnp1 889: doc-flog 1.6 anton 890: doc-falog 1.4 anton 891: doc-fsin 892: doc-fcos 893: doc-fsincos 894: doc-ftan 895: doc-fasin 896: doc-facos 897: doc-fatan 898: doc-fatan2 899: doc-fsinh 900: doc-fcosh 901: doc-ftanh 902: doc-fasinh 903: doc-facosh 904: doc-fatanh 905: 906: @node Stack Manipulation, Memory access, Arithmetic, Words 1.1 anton 907: @section Stack Manipulation 908: 1.17 anton 909: Gforth has a data stack (aka parameter stack) for characters, cells, 1.1 anton 910: addresses, and double cells, a floating point stack for floating point 911: numbers, a return stack for storing the return addresses of colon 912: definitions and other data, and a locals stack for storing local 913: variables. Note that while every sane Forth has a separate floating 914: point stack, this is not strictly required; an ANS Forth system could 915: theoretically keep floating point numbers on the data stack. As an 916: additional difficulty, you don't know how many cells a floating point 917: number takes. It is reportedly possible to write words in a way that 918: they work also for a unified stack model, but we do not recommend trying 1.4 anton 919: it. Instead, just say that your program has an environmental dependency 920: on a separate FP stack. 921: 922: Also, a Forth system is allowed to keep the local variables on the 1.1 anton 923: return stack. This is reasonable, as local variables usually eliminate 924: the need to use the return stack explicitly. So, if you want to produce 925: a standard complying program and if you are using local variables in a 926: word, forget about return stack manipulations in that word (see the 927: standard document for the exact rules). 928: 938: @subsection Data stack 939: doc-drop 940: doc-nip 941: doc-dup 942: doc-over 943: doc-tuck 944: doc-swap 945: doc-rot 946: doc--rot 947: doc-?dup 948: doc-pick 949: doc-roll 950: doc-2drop 951: doc-2nip 952: doc-2dup 953: doc-2over 954: doc-2tuck 955: doc-2swap 956: doc-2rot 957: 1003: @subsection Stack-Memory transfers 1004: 1005: doc-@ 1006: doc-! 1007: doc-+! 1008: doc-c@ 1009: doc-c! 1010: doc-2@ 1011: doc-2! 1012: doc-f@ 1013: doc-f! 1014: doc-sf@ 1015: doc-sf! 1016: doc-df@ 1017: doc-df! 1018: 1.4 anton 1019: @node Address arithmetic, Memory block access, Stack-Memory transfers, Memory access 1.1 anton 1020: @subsection Address arithmetic 1021: 1022: ANS Forth does not specify the sizes of the data types. Instead, it 1023: offers a number of words for computing sizes and doing address 1024: arithmetic. Basically, address arithmetic is performed in terms of 1025: address units (aus); on most systems the address unit is one byte. Note 1026: that a character may have more than one au, so @code{chars} is no noop 1027: (on systems where it is a noop, it compiles to nothing). 1028: 1029: ANS Forth also defines words for aligning addresses for specific 1030: addresses. Many computers require that accesses to specific data types 1031: must only occur at specific addresses; e.g., that cells may only be 1032: accessed at addresses divisible by 4. Even if a machine allows unaligned 1033: accesses, it can usually perform aligned accesses faster. 1034: 1.17 anton 1035: For the performance-conscious: alignment operations are usually only 1.1 anton 1036: necessary during the definition of a data structure, not during the 1037: (more frequent) accesses to it. 1038: 1039: ANS Forth defines no words for character-aligning addresses. This is not 1040: an oversight, but reflects the fact that addresses that are not 1041: char-aligned have no use in the standard and therefore will not be 1042: created. 1043: 1044: The standard guarantees that addresses returned by @code{CREATE}d words 1051: doc-chars 1052: doc-char+ 1053: doc-cells 1054: doc-cell+ 1055: doc-align 1056: doc-aligned 1057: doc-floats 1058: doc-float+ 1059: doc-falign 1060: doc-faligned 1061: doc-sfloats 1062: doc-sfloat+ 1063: doc-sfalign 1064: doc-sfaligned 1065: doc-dfloats 1066: doc-dfloat+ 1067: doc-dfalign 1068: doc-dfaligned 1076: @subsection Memory block access 1077: 1078: doc-move 1079: doc-erase 1080: 1081: While the previous words work on address units, the rest works on 1082: characters. 1083: 1084: doc-cmove 1085: doc-cmove> 1086: doc-fill 1087: doc-blank 1088: 1.4 anton 1089: @node Control Structures, Locals, Memory access, Words 1.1 anton 1090: @section Control Structures 1091: 1092: Control structures in Forth cannot be used in interpret state, only in 1093: compile state, i.e., in a colon definition. We do not like this 1094: limitation, but have not seen a satisfying way around it yet, although 1095: many schemes have been proposed. 1096: 1107: @subsection Selection 1108: 1109: @example 1110: @var{flag} 1111: IF 1112: @var{code} 1113: ENDIF 1114: @end example 1115: or 1116: @example 1117: @var{flag} 1118: IF 1119: @var{code1} 1120: ELSE 1121: @var{code2} 1122: ENDIF 1123: @end example 1124: 1.4 anton 1125: You can use @code{THEN} instead of @code{ENDIF}. Indeed, @code{THEN} is 1.1 anton 1126: standard, and @code{ENDIF} is not, although it is quite popular. We 1127: recommend using @code{ENDIF}, because it is less confusing for people 1128: who also know other languages (and is not prone to reinforcing negative 1129: prejudices against Forth in these people). Adding @code{ENDIF} to a 1130: system that only supplies @code{THEN} is simple: 1131: @example 1132: : endif POSTPONE then ; immediate 1133: @end example 1134: 1135: [According to @cite{Webster's New Encyclopedic Dictionary}, @dfn{then 1136: (adv.)} has the following meanings: 1137: @quotation 1138: ... 2b: following next after in order ... 3d: as a necessary consequence 1139: (if you were there, then you saw them). 1140: @end quotation 1141: Forth's @code{THEN} has the meaning 2b, whereas @code{THEN} in Pascal 1142: and many other programming languages has the meaning 3d.] 1143: 1144: We also provide the words @code{?dup-if} and @code{?dup-0=-if}, so you 1145: can avoid using @code{?dup}. 1146: 1147: @example 1148: @var{n} 1149: CASE 1150: @var{n1} OF @var{code1} ENDOF 1151: @var{n2} OF @var{code2} ENDOF 1.4 anton 1152: @dots{} 1.1 anton 1153: ENDCASE 1154: @end example 1155: 1156: Executes the first @var{codei}, where the @var{ni} is equal to 1157: @var{n}. A default case can be added by simply writing the code after 1158: the last @code{ENDOF}. It may use @var{n}, which is on top of the stack, 1159: but must not consume it. 1160: 1.4 anton 1161: @node Simple Loops, Counted Loops, Selection, Control Structures 1.1 anton 1162: @subsection Simple Loops 1163: 1164: @example 1165: BEGIN 1166: @var{code1} 1167: @var{flag} 1168: WHILE 1169: @var{code2} 1170: REPEAT 1171: @end example 1172: 1173: @var{code1} is executed and @var{flag} is computed. If it is true, 1174: @var{code2} is executed and the loop is restarted; If @var{flag} is false, execution continues after the @code{REPEAT}. 1175: 1176: @example 1177: BEGIN 1178: @var{code} 1179: @var{flag} 1180: UNTIL 1181: @end example 1182: 1183: @var{code} is executed. The loop is restarted if @code{flag} is false. 1184: 1185: @example 1186: BEGIN 1187: @var{code} 1188: AGAIN 1189: @end example 1190: 1191: This is an endless loop. 1192: 1.4 anton 1193: @node Counted Loops, Arbitrary control structures, Simple Loops, Control Structures 1.1 anton 1194: @subsection Counted Loops 1195: 1196: The basic counted loop is: 1197: @example 1198: @var{limit} @var{start} 1199: ?DO 1200: @var{body} 1201: LOOP 1202: @end example 1203: 1204: This performs one iteration for every integer, starting from @var{start} 1205: and up to, but excluding @var{limit}. The counter, aka index, can be 1206: accessed with @code{i}. E.g., the loop 1207: @example 1208: 10 0 ?DO 1209: i . 1210: LOOP 1211: @end example 1212: prints 1213: @example 1214: 0 1 2 3 4 5 6 7 8 9 1215: @end example 1216: The index of the innermost loop can be accessed with @code{i}, the index 1217: of the next loop with @code{j}, and the index of the third loop with 1218: @code{k}. 1219: 1220: The loop control data are kept on the return stack, so there are some 1221: restrictions on mixing return stack accesses and counted loop 1222: words. E.g., if you put values on the return stack outside the loop, you 1223: cannot read them inside the loop. If you put values on the return stack 1224: within a loop, you have to remove them before the end of the loop and 1225: before accessing the index of the loop. 1226: 1227: There are several variations on the counted loop: 1228: 1229: @code{LEAVE} leaves the innermost counted loop immediately. 1230: 1.18 anton 1231: If @var{start} is greater than @var{limit}, a @code{?DO} loop is entered 1232: (and @code{LOOP} iterates until they become equal by wrap-around 1233: arithmetic). This behaviour is usually not what you want. Therefore, 1234: Gforth offers @code{+DO} and @code{U+DO} (as replacements for 1235: @code{?DO}), which do not enter the loop if @var{start} is greater than 1236: @var{limit}; @code{+DO} is for signed loop parameters, @code{U+DO} for 1237: unsigned loop parameters. These words can be implemented easily on 1238: standard systems, so using them does not make your programs hard to 1239: port; e.g.: 1240: @example 1241: : +DO ( compile-time: -- do-sys; run-time: n1 n2 -- ) 1242: POSTPONE over POSTPONE min POSTPONE ?DO ; immediate 1243: @end example 1244: 1259: Therefore we recommend avoiding @code{@var{n} +LOOP} with negative 1260: @var{n}. One alternative is @code{@var{u} -LOOP}, which reduces the 1261: index by @var{u} each iteration. The loop is terminated when the border 1262: between @var{limit+1} and @var{limit} is crossed. Gforth also provides 1263: @code{-DO} and @code{U-DO} for down-counting loops. E.g.: 1274: @code{-2 0 -DO i . -1 S+LOOP} prints @code{0 -1} 1275: 1276: The loop is terminated when the border between @var{limit@minus{}sgn(n)} 1277: and @var{limit} is crossed. Unfortunately, neither @code{-LOOP} nor 1278: @code{S+LOOP} are part of the ANS Forth standard, and they are not easy 1279: to implement using standard words. If you want to write standard 1280: programs, just avoid counting down. 1281: 1282: @code{?DO} can also be replaced by @code{DO}. @code{DO} always enters 1283: the loop, independent of the loop parameters. Do not use @code{DO}, even 1284: if you know that the loop is entered in any case. Such knowledge tends 1285: to become invalid during maintenance of a program, and then the 1286: @code{DO} will make trouble. 1.1 anton 1287: 1288: @code{UNLOOP} is used to prepare for an abnormal loop exit, e.g., via 1289: @code{EXIT}. @code{UNLOOP} removes the loop control parameters from the 1290: return stack so @code{EXIT} can get to its return address. 1291: 1292: Another counted loop is 1293: @example 1294: @var{n} 1295: FOR 1296: @var{body} 1297: NEXT 1298: @end example 1299: This is the preferred loop of native code compiler writers who are. 1304: 1.4 anton 1305: @node Arbitrary control structures, Calls and returns, Counted Loops, Control Structures 1.2 anton 1306: @subsection Arbitrary control structures 1307: 1308: ANS Forth permits and supports using control structures in a non-nested 1309: way. Information about incomplete control structures is stored on the 1310: control-flow stack. This stack may be implemented on the Forth data 1.17 anton 1311: stack, and this is what we have done in Gforth. 1.2 anton: 1.3 anton 1318: doc-if 1319: doc-ahead 1320: doc-then 1321: doc-begin 1322: doc-until 1323: doc-again 1324: doc-cs-pick 1325: doc-cs-roll 1.2 anton 1326: 1.17 anton 1327: On many systems control-flow stack items take one word, in Gforth they 1.2 anton: 1.3 anton 1335: doc-else 1336: doc-while 1337: doc-repeat 1.2 anton 1338: 1357: 1358: The standard does not allow using @code{cs-pick} and @code{cs-roll} on 1359: @i{do-sys}. Our system allows it, but it's your job to ensure that for 1360: every @code{?DO} etc. there is exactly one @code{UNLOOP} on any path 1375: @subsubsection Programming Style 1376: 1377: In order to ensure readability we recommend that you do not create 1378: arbitrary control structures directly, but define new control structure 1379: words for the control structure you want and use these words in your 1380: program. 1381: 1382: E.g., instead of writing 1383: 1384: @example 1385: begin 1386: ... 1387: if [ 1 cs-roll ] 1388: ... 1389: again then 1390: @end example 1391: 1392: we recommend defining control structure words, e.g., 1393: 1394: @example 1395: : while ( dest -- orig dest ) 1396: POSTPONE if 1397: 1 cs-roll ; immediate 1398: 1399: : repeat ( orig dest -- ) 1400: POSTPONE again 1401: POSTPONE then ; immediate 1402: @end example 1403: 1404: and then using these to create the control structure: 1405: 1406: @example 1407: begin 1408: ... 1409: while 1410: ... 1411: repeat 1412: @end example 1413: 1414: That's much easier to read, isn't it? Of course, @code{BEGIN} and 1415: @code{WHILE} are predefined, so in this example it would not be 1416: necessary to define them. 1417:ton 1424: 1425: doc-exit 1426: 1427: Don't forget to clean up the return stack and @code{UNLOOP} any 1428: outstanding @code{?DO}...@code{LOOP}s before @code{EXIT}ing. The 1429: primitive compiled by @code{EXIT} is 1430: 1431: doc-;s 1432: 1442: Local variables can make Forth programming more enjoyable and Forth 1443: programs easier to read. Unfortunately, the locals of ANS Forth are 1444: laden with restrictions. Therefore, we provide not only the ANS Forth 1445: locals wordset, but also our own, more powerful locals wordset (we 1446: implemented the ANS Forth locals wordset through our locals wordset). 1447: 1460: 1461: Locals can be defined with 1462: 1463: @example 1464: @{ local1 local2 ... -- comment @} 1465: @end example 1466: or 1467: @example 1468: @{ local1 local2 ... @} 1469: @end example 1470: 1471: E.g., 1472: @example 1473: : max @{ n1 n2 -- n3 @} 1474: n1 n2 > if 1475: n1 1476: else 1477: n2 1478: endif ; 1479: @end example 1480: 1481: The similarity of locals definitions with stack comments is intended. A 1482: locals definition often replaces the stack comment of a word. The order 1483: of the locals corresponds to the order in a stack comment and everything 1484: after the @code{--} is really a comment. 1485: 1486: This similarity has one disadvantage: It is too easy to confuse locals 1487: declarations with stack comments, causing bugs and making them hard to 1488: find. However, this problem can be avoided by appropriate coding 1489: conventions: Do not use both notations in the same program. If you do, 1490: they should be distinguished using additional means, e.g. by position. 1491: 1492: The name of the local may be preceded by a type specifier, e.g., 1493: @code{F:} for a floating point value: 1494: 1495: @example 1496: : CX* @{ F: Ar F: Ai F: Br F: Bi -- Cr Ci @} 1497: \ complex multiplication 1498: Ar Br f* Ai Bi f* f- 1499: Ar Bi f* Ai Br f* f+ ; 1500: @end example 1501: 1.17 anton 1502: Gforth currently supports cells (@code{W:}, @code{W^}), doubles 1.2 anton 1503: (@code{D:}, @code{D^}), floats (@code{F:}, @code{F^}) and characters 1504: (@code{C:}, @code{C^}) in two flavours: a value-flavoured local (defined 1505: with @code{W:}, @code{D:} etc.) produces its value and can be changed 1506: with @code{TO}. A variable-flavoured local (defined with @code{W^} etc.) 1507: produces its address (which becomes invalid when the variable's scope is 1508: left). E.g., the standard word @code{emit} can be defined in therms of 1509: @code{type} like this: 1510: 1511: @example 1512: : emit @{ C^ char* -- @} 1513: char* 1 type ; 1514: @end example 1515: 1516: A local without type specifier is a @code{W:} local. Both flavours of 1517: locals are initialized with values from the data or FP stack. 1518: 1519: Currently there is no way to define locals with user-defined data 1520: structures, but we are working on it. 1521: 1533: @subsubsection Where are locals visible by name? 1534: 1535: Basically, the answer is that locals are visible where you would expect 1536: it in block-structured languages, and sometimes a little longer. If you 1537: want to restrict the scope of a local, enclose its definition in 1538: @code{SCOPE}...@code{ENDSCOPE}. 1539: 1540: doc-scope 1541: doc-endscope 1542: 1543: These words behave like control structure words, so you can use them 1544: with @code{CS-PICK} and @code{CS-ROLL} to restrict the scope in 1545: arbitrary ways. 1546: 1547: If you want a more exact answer to the visibility question, here's the 1548: basic principle: A local is visible in all places that can only be 1549: reached through the definition of the local@footnote{In compiler 1550: construction terminology, all places dominated by the definition of the 1551: local.}. In other words, it is not visible in places that can be reached 1552: without going through the definition of the local. E.g., locals defined 1553: in @code{IF}...@code{ENDIF} are visible until the @code{ENDIF}, locals 1554: defined in @code{BEGIN}...@code{UNTIL} are visible after the 1555: @code{UNTIL} (until, e.g., a subsequent @code{ENDSCOPE}). 1556: 1557: The reasoning behind this solution is: We want to have the locals 1558: visible as long as it is meaningful. The user can always make the 1559: visibility shorter by using explicit scoping. In a place that can 1560: only be reached through the definition of a local, the meaning of a 1561: local name is clear. In other places it is not: How is the local 1562: initialized at the control flow path that does not contain the 1563: definition? Which local is meant, if the same name is defined twice in 1564: two independent control flow paths? 1565: 1566: This should be enough detail for nearly all users, so you can skip the 1567: rest of this section. If you relly must know all the gory details and 1568: options, read on. 1569: 1570: In order to implement this rule, the compiler has to know which places 1571: are unreachable. It knows this automatically after @code{AHEAD}, 1572: @code{AGAIN}, @code{EXIT} and @code{LEAVE}; in other cases (e.g., after 1573: most @code{THROW}s), you can use the word @code{UNREACHABLE} to tell the 1574: compiler that the control flow never reaches that place. If 1575: @code{UNREACHABLE} is not used where it could, the only consequence is 1576: that the visibility of some locals is more limited than the rule above 1577: says. If @code{UNREACHABLE} is used where it should not (i.e., if you 1578: lie to the compiler), buggy code will be produced. 1579: 1580: Another problem with this rule is that at @code{BEGIN}, the compiler 1.3 anton 1581: does not know which locals will be visible on the incoming 1582: back-edge. All problems discussed in the following are due to this 1583: ignorance of the compiler (we discuss the problems using @code{BEGIN} 1584: loops as examples; the discussion also applies to @code{?DO} and other 1.2 anton 1585: loops). Perhaps the most insidious example is: 1586: @example 1587: AHEAD 1588: BEGIN 1589: x 1590: [ 1 CS-ROLL ] THEN 1.4 anton 1591: @{ x @} 1.2 anton 1592: ... 1593: UNTIL 1594: @end example 1595: 1596: This should be legal according to the visibility rule. The use of 1597: @code{x} can only be reached through the definition; but that appears 1598: textually below the use. 1599: 1600: From this example it is clear that the visibility rules cannot be fully 1601: implemented without major headaches. Our implementation treats common 1602: cases as advertised and the exceptions are treated in a safe way: The 1603: compiler makes a reasonable guess about the locals visible after a 1604: @code{BEGIN}; if it is too pessimistic, the 1605: user will get a spurious error about the local not being defined; if the 1606: compiler is too optimistic, it will notice this later and issue a 1607: warning. In the case above the compiler would complain about @code{x} 1608: being undefined at its use. You can see from the obscure examples in 1609: this section that it takes quite unusual control structures to get the 1610: compiler into trouble, and even then it will often do fine. 1611: 1612: If the @code{BEGIN} is reachable from above, the most optimistic guess 1613: is that all locals visible before the @code{BEGIN} will also be 1614: visible after the @code{BEGIN}. This guess is valid for all loops that 1615: are entered only through the @code{BEGIN}, in particular, for normal 1616: @code{BEGIN}...@code{WHILE}...@code{REPEAT} and 1617: @code{BEGIN}...@code{UNTIL} loops and it is implemented in our 1618: compiler. When the branch to the @code{BEGIN} is finally generated by 1619: @code{AGAIN} or @code{UNTIL}, the compiler checks the guess and 1620: warns the user if it was too optimisitic: 1621: @example 1622: IF 1.4 anton 1623: @{ x @} 1.2 anton 1624: BEGIN 1625: \ x ? 1626: [ 1 cs-roll ] THEN 1627: ... 1628: UNTIL 1629: @end example 1630: 1631: Here, @code{x} lives only until the @code{BEGIN}, but the compiler 1632: optimistically assumes that it lives until the @code{THEN}. It notices 1633: this difference when it compiles the @code{UNTIL} and issues a 1634: warning. The user can avoid the warning, and make sure that @code{x} 1635: is not used in the wrong area by using explicit scoping: 1636: @example 1637: IF 1638: SCOPE 1.4 anton 1639: @{ x @} 1.2 anton 1640: ENDSCOPE 1641: BEGIN 1642: [ 1 cs-roll ] THEN 1643: ... 1644: UNTIL 1645: @end example 1646: 1647: Since the guess is optimistic, there will be no spurious error messages 1648: about undefined locals. 1649: 1650: If the @code{BEGIN} is not reachable from above (e.g., after 1651: @code{AHEAD} or @code{EXIT}), the compiler cannot even make an 1652: optimistic guess, as the locals visible after the @code{BEGIN} may be 1653: defined later. Therefore, the compiler assumes that no locals are 1664: AHEAD 1665: ASSUME-LIVE 1666: BEGIN 1667: x 1668: [ 1 CS-ROLL ] THEN 1669: ... 1670: UNTIL 1671: @end example 1672: 1673: Other cases where the locals are defined before the @code{BEGIN} can be 1674: handled by inserting an appropriate @code{CS-ROLL} before the 1675: @code{ASSUME-LIVE} (and changing the control-flow stack manipulation 1676: behind the @code{ASSUME-LIVE}). 1677: 1678: Cases where locals are defined after the @code{BEGIN} (but should be 1679: visible immediately after the @code{BEGIN}) can only be handled by 1680: rearranging the loop. E.g., the ``most insidious'' example above can be 1681: arranged into: 1682: @example 1683: BEGIN 1692: @subsubsection How long do locals live? 1693: 1694: The right answer for the lifetime question would be: A local lives at 1695: least as long as it can be accessed. For a value-flavoured local this 1696: means: until the end of its visibility. However, a variable-flavoured 1697: local could be accessed through its address far beyond its visibility 1698: scope. Ultimately, this would mean that such locals would have to be 1699: garbage collected. Since this entails un-Forth-like implementation 1700: complexities, I adopted the same cowardly solution as some other 1701: languages (e.g., C): The local lives only as long as it is visible; 1702: afterwards its address is invalid (and programs that access it 1703: afterwards are erroneous). 1704: 1.17 anton 1705: @node Programming Style, Implementation, How long do locals live?, Gforth locals 1.2 anton 1706: @subsubsection Programming Style 1707: 1708: The freedom to define locals anywhere has the potential to change 1709: programming styles dramatically. In particular, the need to use the 1710: return stack for intermediate storage vanishes. Moreover, all stack 1711: manipulations (except @code{PICK}s and @code{ROLL}s with run-time 1712: determined arguments) can be eliminated: If the stack items are in the 1713: wrong order, just write a locals definition for all of them; then 1714: write the items in the order you want. 1715: 1716: This seems a little far-fetched and eliminating stack manipulations is 1721: 1722: This shows one potential benefit of locals: making Forth programs more 1723: readable. Of course, this benefit will only be realized if the 1724: programmers continue to honour the principle of factoring instead of 1725: using the added latitude to make the words longer. 1726: 1727: Using @code{TO} can and should be avoided. Without @code{TO}, 1728: every value-flavoured local has only a single assignment and many 1729: advantages of functional languages apply to Forth. I.e., programs are 1730: easier to analyse, to optimize and to read: It is clear from the 1731: definition what the local stands for, it does not turn into something 1732: different later. 1733: 1734: E.g., a definition using @code{TO} might look like this: 1735: @example 1736: : strcmp @{ addr1 u1 addr2 u2 -- n @} 1737: u1 u2 min 0 1738: ?do 1739: addr1 c@ addr2 c@ - ?dup 1740: if 1741: unloop exit 1742: then 1743: addr1 char+ TO addr1 1744: addr2 char+ TO addr2 1745: loop 1746: u1 u2 - ; 1747: @end example 1748: Here, @code{TO} is used to update @code{addr1} and @code{addr2} at 1749: every loop iteration. @code{strcmp} is a typical example of the 1750: readability problems of using @code{TO}. When you start reading 1751: @code{strcmp}, you think that @code{addr1} refers to the start of the 1752: string. Only near the end of the loop you realize that it is something 1753: else. 1754: 1755: This can be avoided by defining two locals at the start of the loop that 1756: are initialized with the right value for the current iteration. 1757: @example 1758: : strcmp @{ addr1 u1 addr2 u2 -- n @} 1759: addr1 addr2 1760: u1 u2 min 0 1761: ?do @{ s1 s2 @} 1762: s1 c@ s2 c@ - ?dup 1763: if 1764: unloop exit 1765: then 1766: s1 char+ s2 char+ 1767: loop 1768: 2drop 1769: u1 u2 - ; 1770: @end example 1771: Here it is clear from the start that @code{s1} has a different value 1772: in every loop iteration. 1773: 1.17 anton 1774: @node Implementation, , Programming Style, Gforth locals 1.2 anton 1775: @subsubsection Implementation 1776: 1.17 anton 1777: Gforth uses an extra locals stack. The most compelling reason for 1.2 anton 1778: this is that the return stack is not float-aligned; using an extra stack 1779: also eliminates the problems and restrictions of using the return stack 1780: as locals stack. Like the other stacks, the locals stack grows toward 1781: lower addresses. A few primitives allow an efficient implementation: 1782: 1783: doc-@local# 1784: doc-f@local# 1785: doc-laddr# 1786: doc-lp+!# 1787: doc-lp! 1788: doc->l 1789: doc-f>l 1790: 1791: In addition to these primitives, some specializations of these 1792: primitives for commonly occurring inline arguments are provided for 1793: efficiency reasons, e.g., @code{@@local0} as specialization of 1794: @code{@@local#} for the inline argument 0. The following compiling words 1795: compile the right specialized version, or the general version, as 1796: appropriate: 1797: 1.12 anton 1798: doc-compile-@local 1799: doc-compile-f@local 1.2 anton 1800: doc-compile-lp+! 1801: 1802: Combinations of conditional branches and @code{lp+!#} like 1803: @code{?branch-lp+!#} (the locals pointer is only changed if the branch 1804: is taken) are provided for efficiency and correctness in loops. 1805: 1806: A special area in the dictionary space is reserved for keeping the 1807: local variable names. @code{@{} switches the dictionary pointer to this 1808: area and @code{@}} switches it back and generates the locals 1809: initializing code. @code{W:} etc.@ are normal defining words. This 1810: special area is cleared at the start of every colon definition. 18 1816: with a special search method: When it is searched for a word, it 1817: actually creates that word using @code{W:}. @code{@{} changes the search 1818: order to first search the wordlist containing @code{@}}, @code{W:} etc., 1819: and then the wordlist for defining locals without type specifiers. 1820: 1821: The lifetime rules support a stack discipline within a colon 1822: definition: The lifetime of a local is either nested with other locals 1823: lifetimes or it does not overlap them. 1824: 1825: At @code{BEGIN}, @code{IF}, and @code{AHEAD} no code for locals stack 1826: pointer manipulation is generated. Between control structure words 1827: locals definitions can push locals onto the locals stack. @code{AGAIN} 1828: is the simplest of the other three control flow words. It has to 1829: restore the locals stack depth of the corresponding @code{BEGIN} 1830: before branching. The code looks like this: 1831: @format 1832: @code{lp+!#} current-locals-size @minus{} dest-locals-size 1833: @code{branch} <begin> 1834: @end format 1835: 1836: @code{UNTIL} is a little more complicated: If it branches back, it 1837: must adjust the stack just like @code{AGAIN}. But if it falls through, 1838: the locals stack must not be changed. The compiler generates the 1839: following code: 1840: @format 1841: @code{?branch-lp+!#} <begin> current-locals-size @minus{} dest-locals-size 1842: @end format 1843: The locals stack pointer is only adjusted if the branch is taken. 1844: 1845: @code{THEN} can produce somewhat inefficient code: 1846: @format 1847: @code{lp+!#} current-locals-size @minus{} orig-locals-size 1848: <orig target>: 1849: @code{lp+!#} orig-locals-size @minus{} new-locals-size 1850: @end format 1851: The second @code{lp+!#} adjusts the locals stack pointer from the 1.4 anton 1852: level at the @var{orig} point to the level after the @code{THEN}. The 1.2 anton 1853: first @code{lp+!#} adjusts the locals stack pointer from the current 1854: level to the level at the orig point, so the complete effect is an 1855: adjustment from the current level to the right level after the 1856: @code{THEN}. 1857: 1858: In a conventional Forth implementation a dest control-flow stack entry 1859: is just the target address and an orig entry is just the address to be 1860: patched. Our locals implementation adds a wordlist to every orig or dest 1861: item. It is the list of locals visible (or assumed visible) at the point 1862: described by the entry. Our implementation also adds a tag to identify 1863: the kind of entry, in particular to differentiate between live and dead 1864: (reachable and unreachable) orig entries. 1865: 1866: A few unusual operations have to be performed on locals wordlists: 1867: 1868: doc-common-list 1869: doc-sub-list? 1870: doc-list-size 1871: 1872: Several features of our locals wordlist implementation make these 1873: operations easy to implement: The locals wordlists are organised as 1874: linked lists; the tails of these lists are shared, if the lists 1875: contain some of the same locals; and the address of a name is greater 1876: than the address of the names behind it in the list. 1877: 1878: Another important implementation detail is the variable 1879: @code{dead-code}. It is used by @code{BEGIN} and @code{THEN} to 1880: determine if they can be reached directly or only through the branch 1881: that they resolve. @code{dead-code} is set by @code{UNREACHABLE}, 1882: @code{AHEAD}, @code{EXIT} etc., and cleared at the start of a colon 1883: definition, by @code{BEGIN} and usually by @code{THEN}. 1884: 1885: Counted loops are similar to other loops in most respects, but 1886: @code{LEAVE} requires special attention: It performs basically the same 1887: service as @code{AHEAD}, but it does not create a control-flow stack 1888: entry. Therefore the information has to be stored elsewhere; 1889: traditionally, the information was stored in the target fields of the 1890: branches created by the @code{LEAVE}s, by organizing these fields into a 1891: linked list. Unfortunately, this clever trick does not provide enough 1892: space for storing our extended control flow information. Therefore, we 1893: introduce another stack, the leave stack. It contains the control-flow 1894: stack entries for all unresolved @code{LEAVE}s. 1895: 1896: Local names are kept until the end of the colon definition, even if 1897: they are no longer visible in any control-flow path. In a few cases 1898: this may lead to increased space needs for the locals name area, but 1899: usually less than reclaiming this space would cost in code size. 1900: 1901: 1941: anything to use it. If you want to port a program using this syntax to 1942: another ANS Forth system, use @file{anslocal.fs} to implement the syntax 1943: on the other system. 1944: 1945: Note that a syntax shown in the standard, section A.13 looks 1946: similar, but is quite different in having the order of locals 1947: reversed. Beware! 1948: 1949: The ANS Forth locals wordset itself consists of the following word 1950: 1951: doc-(local) 1952: 1953: The ANS Forth locals extension wordset defines a syntax, but it is so 1954: awful that we strongly recommend not to use it. We have implemented this 1.17 anton 1955: syntax to make porting to Gforth easy, but do not document it here. The 1.2 anton 1956: problem with this syntax is that the locals are defined in an order 1957: reversed with respect to the standard stack comment notation, making 1958: programs harder to read, and easier to misread and miswrite. The only 1959: merit of this syntax is that it is easy to implement using the ANS Forth 1960: locals wordset. 1.3 anton 1961: 1.4 anton 1962: @node Defining Words, Wordlists, Locals, Words 1963: @section Defining Words 1964: 1.14 anton 1965: @menu 1966: * Values:: 1967: @end menu 1968: 1.4 anton 1969: @node Values, , Defining Words, Defining Words 1970: @subsection Values 1971: 1972: @node Wordlists, Files, Defining Words, Words 1973: @section Wordlists 1974: 1975: @node Files, Blocks, Wordlists, Words 1976: @section Files 1977: 1978: @node Blocks, Other I/O, Files, Words 1979: @section Blocks 1980: 1981: @node Other I/O, Programming Tools, Blocks, Words 1982: @section Other I/O 1983: 1993: @subsection Debugging 1994: 1995: The simple debugging aids provided in @file{debugging.fs} 1996: are meant to support a different style of debugging than the 1997: tracing/stepping debuggers used in languages with long turn-around 1998: times. 1999: 2000: A much better (faster) way in fast-compilig languages is to add 2001: printing code at well-selected places, let the program run, look at 2002: the output, see where things went wrong, add more printing code, etc., 2003: until the bug is found. 2004: 2005: The word @code{~~} is easy to insert. It just prints debugging 2006: information (by default the source location and the stack contents). It 2007: is also easy to remove (@kbd{C-x ~} in the Emacs Forth mode to 2008: query-replace them with nothing). The deferred words 2009: @code{printdebugdata} and @code{printdebugline} control the output of 2010: @code{~~}. The default source location output format works well with 2011: Emacs' compilation mode, so you can step through the program at the 2030: assertions for this purpose. They are used like this: 2031: 2032: @example 2033: assert( @var{flag} ) 2034: @end example 2035: 2036: The code between @code{assert(} and @code{)} should compute a flag, that 2037: should be true if everything is alright and false otherwise. It should 2038: not change anything else on the stack. The overall stack effect of the 2039: assertion is @code{( -- )}. E.g. 2040: 2041: @example 2042: assert( 1 1 + 2 = ) \ what we learn in school 2043: assert( dup 0<> ) \ assert that the top of stack is not zero 2044: assert( false ) \ this code should not be reached 2045: @end example 2046: 2047: The need for assertions is different at different times. During 2048: debugging, we want more checking, in production we sometimes care more 2049: for speed. Therefore, assertions can be turned off, i.e., the assertion 2050: becomes a comment. Depending on the importance of an assertion and the 2051: time it takes to check it, you may want to turn off some assertions and 1.17 anton 2052: keep others turned on. Gforth provides several levels of assertions for 1.5 anton 2053: this purpose: 2054: 2055: doc-assert0( 2056: doc-assert1( 2057: doc-assert2( 2058: doc-assert3( 2059: doc-assert( 2060: doc-) 2061: 2062: @code{Assert(} is the same as @code{assert1(}. The variable 2063: @code{assert-level} specifies the highest assertions that are turned 2064: on. I.e., at the default @code{assert-level} of one, @code{assert0(} and 2065: @code{assert1(} assertions perform checking, while @code{assert2(} and 2066: @code{assert3(} assertions are treated as comments. 2067: 2068: Note that the @code{assert-level} is evaluated at compile-time, not at 2069: run-time. I.e., you cannot turn assertions on or off at run-time, you 2070: have to set the @code{assert-level} appropriately before compiling a 2071: piece of code. You can compile several pieces of code at several 2072: @code{assert-level}s (e.g., a trusted library at level 1 and newly 2073: written code at level 3). 2074: 2075: doc-assert-level 2076: 2077: If an assertion fails, a message compatible with Emacs' compilation mode 2078: is produced and the execution is aborted (currently with @code{ABORT"}. 2079: If there is interest, we will introduce a special throw code. But if you 2080: intend to @code{catch} a specific condition, using @code{throw} is 2081: probably more appropriate than an assertion). 2082: 1.18 anton 2083: @node Assembler and Code words, Threading Words, Programming Tools, Words 2084: @section Assembler and Code words 2085: 2086: Gforth provides some words for defining primitives (words written in 2087: machine code), and for defining the the machine-code equivalent of 2088: @code{DOES>}-based defining words. However, the machine-independent 2089: nature of Gforth poses a few problems: First of all. Gforth runs on 2090: several architectures, so it can provide no standard assembler. What's 2091: worse is that the register allocation not only depends on the processor, 1.25 ! anton 2092: but also on the @code{gcc} version and options used. 1.18 anton 2093: 1.25 ! anton 2094: The words that Gforth offers encapsulate some system dependences (e.g., the 1.18 anton 2095: header structure), so a system-independent assembler may be used in 2096: Gforth. If you do not have an assembler, you can compile machine code 2097: directly with @code{,} and @code{c,}. 2098: 2099: doc-assembler 2100: doc-code 2101: doc-end-code 2102: doc-;code 2103: doc-flush-icache 2104: 2105: If @code{flush-icache} does not work correctly, @code{code} words 2106: etc. will not work (reliably), either. 2107: 2108: These words are rarely used. Therefore they reside in @code{code.fs}, 2109: which is usually not loaded (except @code{flush-icache}, which is always 1.19 anton 2110: present). You can load them with @code{require code.fs}. 1.18 anton 2111: 1.25 ! anton 2112: In the assembly code you will want to refer to the inner interpreter's ! 2113: registers (e.g., the data stack pointer) and you may want to use other ! 2114: registers for temporary storage. Unfortunately, the register allocation ! 2115: is installation-dependent. ! 2116: ! 2117: The easiest solution is to use explicit register declarations ! 2118: (@pxref{Explicit Reg Vars, , Variables in Specified Registers, gcc.info, ! 2119: GNU C Manual}) for all of the inner interpreter's registers: You have to ! 2120: compile Gforth with @code{-DFORCE_REG} (configure option ! 2121: @code{--enable-force-reg}) and the appropriate declarations must be ! 2122: present in the @code{machine.h} file (see @code{mips.h} for an example; ! 2123: you can find a full list of all declarable register symbols with ! 2124: @code{grep register engine.c}). If you give explicit registers to all ! 2125: variables that are declared at the beginning of @code{engine()}, you ! 2126: should be able to use the other caller-saved registers for temporary ! 2127: storage. Alternatively, you can use the @code{gcc} option ! 2128: @code{-ffixed-REG} (@pxref{Code Gen Options, , Options for Code ! 2129: Generation Conventions, gcc.info, GNU C Manual}) to reserve a register ! 2130: (however, this restriction on register allocation may slow Gforth ! 2131: significantly). ! 2132: ! 2133: If this solution is not viable (e.g., because @code{gcc} does not allow ! 2134: you to explicitly declare all the registers you need), you have to find ! 2135: out by looking at the code where the inner interpreter's registers ! 2136: reside and which registers can be used for temporary storage. You can ! 2137: get an assembly listing of the engine's code with @code{make engine.s}. ! 2138: ! 2139: In any case, it is good practice to abstract your assembly code from the ! 2140: actual register allocation. E.g., if the data stack pointer resides in ! 2141: register @code{$17}, create an alias for this register called @code{sp}, ! 2142: and use that in your assembly code. ! 2143: 2156: abstracts away the differences between direct and indirect threading 2157: (and, for direct threading, the machine dependences). However, at 2158: present this wordset is still inclomplete. It is also pretty low-level; 2159: some day it will hopefully be made unnecessary by an internals words set 2160: that abstracts implementation details away completely. 2161: 2162: doc->code-address 2163: doc->does-code 2164: doc-code-address! 2165: doc-does-code! 2166: doc-does-handler! 2167: doc-/does-handler 2168: 1.18 anton 2169: The code addresses produced by various defining words are produced by 2170: the following words: 1.14 anton 2171: 1.18 anton 2172: doc-docol: 2173: doc-docon: 2174: doc-dovar: 2175: doc-douser: 2176: doc-dodefer: 2177: doc-dofield: 2178: 2179: Currently there is no installation-independent way for recogizing words 2180: defined by a @code{CREATE}...@code{DOES>} word; however, once you know 2181: that a word is defined by a @code{CREATE}...@code{DOES>} word, you can 2182: use @code{>DOES-CODE}. 2189: ANS Forth System 2190: @itemize 2191: @item providing the Core Extensions word set 2192: @item providing the Block word set 2193: @item providing the Block Extensions word set 2194: @item providing the Double-Number word set 2195: @item providing the Double-Number Extensions word set 2196: @item providing the Exception word set 2197: @item providing the Exception Extensions word set 2198: @item providing the Facility word set 2199: @item providing @code{MS} and @code{TIME&DATE} from the Facility Extensions word set 2200: @item providing the File Access word set 2201: @item providing the File Access Extensions word set 2202: @item providing the Floating-Point word set 2203: @item providing the Floating-Point Extensions word set 2204: @item providing the Locals word set 2205: @item providing the Locals Extensions word set 2206: @item providing the Memory-Allocation word set 2207: @item providing the Memory-Allocation Extensions word set (that one's easy) 2208: @item providing the Programming-Tools word set 1.18 anton 2209: @item providing @code{;code}, @code{AHEAD}, @code{ASSEMBLER}, @code{BYE}, @code{CODE}, @code{CS-PICK}, @code{CS-ROLL}, @code{STATE}, @code{[ELSE]}, @code{[IF]}, @code{[THEN]} from the Programming-Tools Extensions word set 1.15 anton 2210: @item providing the Search-Order word set 2211: @item providing the Search-Order Extensions word set 2212: @item providing the String word set 2213: @item providing the String Extensions word set (another easy one) 2214: @end itemize 2215: 2216: In addition, ANS Forth systems are required to document certain 2217: implementation choices. This chapter tries to meet these 2218: requirements. In many cases it gives a way to ask the system for the 2219: information instead of providing the information directly, in 2220: particular, if the information depends on the processor, the operating 2221: system or the installation options chosen, or if they are likely to 1.17 anton 2222: change during the maintenance of Gforth. 1.15 anton 2223: 1.14 anton 2224: @comment The framework for the rest has been taken from pfe. 2225: 2226: @menu 2227: * The Core Words:: 2228: * The optional Block word set:: 2229: * The optional Double Number word set:: 2230: * The optional Exception word set:: 2231: * The optional Facility word set:: 2232: * The optional File-Access word set:: 2233: * The optional Floating-Point word set:: 2234: * The optional Locals word set:: 2235: * The optional Memory-Allocation word set:: 2236: * The optional Programming-Tools word set:: 2237: * The optional Search-Order word set:: 2238: @end menu 2239: 2240: 2241: @c ===================================================================== 2242: @node The Core Words, The optional Block word set, ANS conformance, ANS conformance 2243: @comment node-name, next, previous, up 2244: @section The Core Words 2245: @c ===================================================================== 2246: 2247: @menu 2262: (e.g., an address aligned for a datum of size 8 is divisible by 2263: 8). Unaligned accesses usually result in a @code{-23 THROW}. 2264: 2265: @item @code{EMIT} and non-graphic characters: 2266: The character is output using the C library function (actually, macro) 2267: @code{putchar}. 2268: 2269: @item character editing of @code{ACCEPT} and @code{EXPECT}: 2270: This is modeled on the GNU readline library (@pxref{Readline 2271: Interaction, , Command Line Editing, readline, The GNU Readline 2272: Library}) with Emacs-like key bindings. @kbd{Tab} deviates a little by 2273: producing a full word completion every time you type it (instead of 2274: producing the common prefix of all completions). 2275: 2276: @item character set: 2277: The character set of your computer and display device. Gforth is 2278: 8-bit-clean (but some other component in your system may make trouble). 2279: 2280: @item Character-aligned address requirements: 2281: installation-dependent. Currently a character is represented by a C 2282: @code{unsigned char}; in the future we might switch to @code{wchar_t} 2283: (Comments on that requested). 2284: 2285: @item character-set extensions and matching of names: 1.17 anton 2286: Any character except the ASCII NUL charcter can be used in a 2287: name. Matching is case-insensitive. The matching is performed using the 2288: C function @code{strncasecmp}, whose function is probably influenced by 2289: the locale. E.g., the @code{C} locale does not know about accents and 1.14 anton 2290: umlauts, so they are matched case-sensitively in that locale. For 2291: portability reasons it is best to write programs such that they work in 2292: the @code{C} locale. Then one can use libraries written by a Polish 2293: programmer (who might use words containing ISO Latin-2 encoded 2294: characters) and by a French programmer (ISO Latin-1) in the same program 2295: (of course, @code{WORDS} will produce funny results for some of the 2296: words (which ones, depends on the font you are using)). Also, the locale 2297: you prefer may not be available in other operating systems. Hopefully, 2298: Unicode will solve these problems one day. 2299: 2300: @item conditions under which control characters match a space delimiter: 2301: If @code{WORD} is called with the space character as a delimiter, all 2302: white-space characters (as identified by the C macro @code{isspace()}) 2303: are delimiters. @code{PARSE}, on the other hand, treats space like other 2304: delimiters. @code{PARSE-WORD} treats space like @code{WORD}, but behaves 2305: like @code{PARSE} otherwise. @code{(NAME)}, which is used by the outer 2306: interpreter (aka text interpreter) by default, treats all white-space 2307: characters as delimiters. 2308: 2309: @item format of the control flow stack: 2310: The data stack is used as control flow stack. The size of a control flow 2311: stack item in cells is given by the constant @code{cs-item-size}. At the 2312: time of this writing, an item consists of a (pointer to a) locals list 2313: (third), an address in the code (second), and a tag for identifying the 2314: item (TOS). The following tags are used: @code{defstart}, 2315: @code{live-orig}, @code{dead-orig}, @code{dest}, @code{do-dest}, 2316: @code{scopestart}. 2317: 2318: @item conversion of digits > 35 2319: The characters @code{[\]^_'} are the digits with the decimal value 2320: 36@minus{}41. There is no way to input many of the larger digits. 2321: 2322: @item display after input terminates in @code{ACCEPT} and @code{EXPECT}: 2323: The cursor is moved to the end of the entered string. If the input is 2324: terminated using the @kbd{Return} key, a space is typed. 2325: 2326: @item exception abort sequence of @code{ABORT"}: 2327: The error string is stored into the variable @code{"error} and a 2328: @code{-2 throw} is performed. 2329: 2330: @item input line terminator: 2331: For interactive input, @kbd{C-m} and @kbd{C-j} terminate lines. One of 2332: these characters is typically produced when you type the @kbd{Enter} or 2333: @kbd{Return} key. 2334: 2335: @item maximum size of a counted string: 2336: @code{s" /counted-string" environment? drop .}. Currently 255 characters 2337: on all ports, but this may change. 2338: 2339: @item maximum size of a parsed string: 2340: Given by the constant @code{/line}. Currently 255 characters. 2341: 2342: @item maximum size of a definition name, in characters: 2343: 31 2344: 2345: @item maximum string length for @code{ENVIRONMENT?}, in characters: 2346: 31 2347: 2348: @item method of selecting the user input device: 2362: 2363: @item number of bits in one address unit: 2364: @code{s" address-units-bits" environment? drop .}. 8 in all current 2365: ports. 2366: 2367: @item number representation and arithmetic: 2368: Processor-dependent. Binary two's complement on all current ports. 2369: 2370: @item ranges for integer types: 2371: Installation-dependent. Make environmental queries for @code{MAX-N}, 2372: @code{MAX-U}, @code{MAX-D} and @code{MAX-UD}. The lower bounds for 2373: unsigned (and positive) types is 0. The lower bound for signed types on 2374: two's complement and one's complement machines machines can be computed 2375: by adding 1 to the upper bound. 2376: 2377: @item read-only data space regions: 2378: The whole Forth data space is writable. 2379: 2380: @item size of buffer at @code{WORD}: 2381: @code{PAD HERE - .}. 104 characters on 32-bit machines. The buffer is 2382: shared with the pictured numeric output string. If overwriting 2383: @code{PAD} is acceptable, it is as large as the remaining dictionary 2384: space, although only as much can be sensibly used as fits in a counted 2385: string. 2386: 2387: @item size of one cell in address units: 2388: @code{1 cells .}. 2389: 2390: @item size of one character in address units: 2391: @code{1 chars .}. 1 on all current ports. 2392: 2393: @item size of the keyboard terminal buffer: 2394: Varies. You can determine the size at a specific time using @code{lp@ 2395: tib - .}. It is shared with the locals stack and TIBs of files that 2396: include the current file. You can change the amount of space for TIBs 1.17 anton 2397: and locals stack at Gforth startup with the command line option 1.14 anton 2398: @code{-l}. 2399: 2400: @item size of the pictured numeric output buffer: 2401: @code{PAD HERE - .}. 104 characters on 32-bit machines. The buffer is 2402: shared with @code{WORD}. 2403: 2404: @item size of the scratch area returned by @code{PAD}: 2405: The remainder of dictionary space. You can even use the unused part of 2406: the data stack space. The current size can be computed with @code{sp@ 2407: pad - .}. 2408: 2409: @item system case-sensitivity characteristics: 2410: Dictionary searches are case insensitive. However, as explained above 2411: under @i{character-set extensions}, the matching for non-ASCII 2412: characters is determined by the locale you are using. In the default 2413: @code{C} locale all non-ASCII characters are matched case-sensitively. 2414: 2415: @item system prompt: 2416: @code{ ok} in interpret state, @code{ compiled} in compile state. 2417: 2418: @item division rounding: 2419: installation dependent. @code{s" floored" environment? drop .}. We leave 1.25 ! anton 2420: the choice to @code{gcc} (what to use for @code{/}) and to you (whether to use 1.14 anton 2421: @code{fm/mod}, @code{sm/rem} or simply @code{/}). 2422: 2423: @item values of @code{STATE} when true: 2424: -1. 2425: 2426: @item values returned after arithmetic overflow: 2427: On two's complement machines, arithmetic is performed modulo 2428: 2**bits-per-cell for single arithmetic and 4**bits-per-cell for double 2429: arithmetic (with appropriate mapping for signed types). Division by zero 2430: typically results in a @code{-55 throw} (floatingpoint unidentified 2431: fault), although a @code{-10 throw} (divide by zero) would be more 2432: appropriate. 2433: 2434: @item whether the current definition can be found after @t{DOES>}: 2435: No. 2436: 2437: @end table 2438: 2439: @c --------------------------------------------------------------------- 2440: @node core-ambcond, core-other, core-idef, The Core Words 2441: @subsection Ambiguous conditions 2442: @c --------------------------------------------------------------------- 2443: 2444: @table @i 2445: 2446: @item a name is neither a word nor a number: 2447: @code{-13 throw} (Undefined word) 2448: 2449: @item a definition name exceeds the maximum length allowed: 2450: @code{-19 throw} (Word name too long) 2451: 2452: @item addressing a region not inside the various data spaces of the forth system: 2453: The stacks, code space and name space are accessible. Machine code space is 2454: typically readable. Accessing other addresses gives results dependent on 2455: the operating system. On decent systems: @code{-9 throw} (Invalid memory 2456: address). 2457: 2458: @item argument type incompatible with parameter: 2459: This is usually not caught. Some words perform checks, e.g., the control 2460: flow words, and issue a @code{ABORT"} or @code{-12 THROW} (Argument type 2461: mismatch). 2462: 2463: @item attempting to obtain the execution token of a word with undefined execution semantics: 2464: You get an execution token representing the compilation semantics 2465: instead. 2466: 2467: @item dividing by zero: 2468: typically results in a @code{-55 throw} (floating point unidentified 2469: fault), although a @code{-10 throw} (divide by zero) would be more 2470: appropriate. 2471: 2472: @item insufficient data stack or return stack space: 2473: Not checked. This typically results in mysterious illegal memory 2474: accesses, producing @code{-9 throw} (Invalid memory address) or 2475: @code{-23 throw} (Address alignment exception). 2476: 2477: @item insufficient space for loop control parameters: 2478: like other return stack overflows. 2479: 2480: @item insufficient space in the dictionary: 2481: Not checked. Similar results as stack overflows. However, typically the 2482: error appears at a different place when one inserts or removes code. 2483: 2484: @item interpreting a word with undefined interpretation semantics: 2485: For some words, we defined interpretation semantics. For the others: 2486: @code{-14 throw} (Interpreting a compile-only word). Note that this is 2487: checked only by the outer (aka text) interpreter; if the word is 2488: @code{execute}d in some other way, it will typically perform it's 2489: compilation semantics even in interpret state. (We could change @code{'} 2490: and relatives not to give the xt of such words, but we think that would 2491: be too restrictive). 2492: 2493: @item modifying the contents of the input buffer or a string literal: 2494: These are located in writable memory and can be modified. 2495: 2496: @item overflow of the pictured numeric output string: 2497: Not checked. 2498: 2499: @item parsed string overflow: 2500: @code{PARSE} cannot overflow. @code{WORD} does not check for overflow. 2501: 2502: @item producing a result out of range: 2503: On two's complement machines, arithmetic is performed modulo 2504: 2**bits-per-cell for single arithmetic and 4**bits-per-cell for double 2505: arithmetic (with appropriate mapping for signed types). Division by zero 2506: typically results in a @code{-55 throw} (floatingpoint unidentified 2507: fault), although a @code{-10 throw} (divide by zero) would be more 2508: appropriate. @code{convert} and @code{>number} currently overflow 2509: silently. 2510: 2511: @item reading from an empty data or return stack: 2512: The data stack is checked by the outer (aka text) interpreter after 2513: every word executed. If it has underflowed, a @code{-4 throw} (Stack 2514: underflow) is performed. Apart from that, the stacks are not checked and 2515: underflows can result in similar behaviour as overflows (of adjacent 2516: stacks). 2517: 2518: @item unexepected end of the input buffer, resulting in an attempt to use a zero-length string as a name: 2519: @code{Create} and its descendants perform a @code{-16 throw} (Attempt to 2520: use zero-length string as a name). Words like @code{'} probably will not 2521: find what they search. Note that it is possible to create zero-length 2522: names with @code{nextname} (should it not?). 2523: 2524: @item @code{>IN} greater than input buffer: 2525: The next invocation of a parsing word returns a string wih length 0. 2526: 2527: @item @code{RECURSE} appears after @code{DOES>}: 2528: Compiles a recursive call to the defining word not to the defined word. 2529: 2530: @item argument input source different than current input source for @code{RESTORE-INPUT}: 2531: !!???If the argument input source is a valid input source then it gets 1.19 anton 2532: restored. Otherwise causes @code{-12 THROW}, which, unless caught, issues 1.14 anton 2533: the message "argument type mismatch" and aborts.: 1.15 anton 2562: @item name not found (@code{'}, @code{POSTPONE}, @code{[']}, @code{[COMPILE]}): 1.14 anton: 1.15 anton 2577: @item u greater than or equal to the number of bits in a cell (@code{LSHIFT}, @code{RSHIFT}): 1.14 anton: !!?? 2606: 2607: @item program data space available: 2608: @code{sp@ here - .} gives the space remaining for dictionary and data 2609: stack together. 2610: 2611: @item return stack space available: 2612: !!?? 2613: 2614: @item stack space available: 2615: @code{sp@ here - .} gives the space remaining for dictionary and data 2616: stack together. 2617: 2618: @item system dictionary space required, in address units: 2619: Type @code{here forthstart - .} after startup. At the time of this 2620: writing, this gives 70108 (bytes) on a 32-bit system. 2621: @end table 2622: 2623: 2624: @c ===================================================================== 2625: @node The optional Block word set, The optional Double Number word set, The Core Words, ANS conformance 2626: @section The optional Block word set 2627: @c ===================================================================== 2628: 2629: @menu 1.15 anton 2630: * block-idef:: Implementation Defined Options 2631: * block-ambcond:: Ambiguous Conditions 2632: * block-other:: Other System Documentation 1.14 anton 2633: @end menu 2634: 2635: 2636: @c --------------------------------------------------------------------- 2637: @node block-idef, block-ambcond, The optional Block word set, The optional Block word set 2638: @subsection Implementation Defined Options 2639: @c --------------------------------------------------------------------- 2640: 2641: @table @i 2642: 2643: @item the format for display by @code{LIST}: 2644: First the screen number is displayed, then 16 lines of 64 characters, 2645: each line preceded by the line number. 2646: 2647: @item the length of a line affected by @code{\}: 2648: 64 characters. 2649: @end table 2650: 2651: 2652: @c --------------------------------------------------------------------- 2653: @node block-ambcond, block-other, block-idef, The optional Block word set 2654: @subsection Ambiguous conditions 2655: @c --------------------------------------------------------------------- 2656: 2657: @table @i 2658: 2659: @item correct block read was not possible: 2660: Typically results in a @code{throw} of some OS-derived value (between 2661: -512 and -2048). If the blocks file was just not long enough, blanks are 2662: supplied for the missing portion. 2663: 2664: @item I/O exception in block transfer: 2665: Typically results in a @code{throw} of some OS-derived value (between 2666: -512 and -2048). 2667: 2668: @item invalid block number: 2669: @code{-35 throw} (Invalid block number) 2670: 2671: @item a program directly alters the contents of @code{BLK}: 2672: The input stream is switched to that other block, at the same 2673: position. If the storing to @code{BLK} happens when interpreting 2674: non-block input, the system will get quite confused when the block ends. 2675: 2676: @item no current block buffer for @code{UPDATE}: 2677: @code{UPDATE} has no effect. 2678: 2679: @end table 2680: 2681: 2682: @c --------------------------------------------------------------------- 2683: @node block-other, , block-ambcond, The optional Block word set 2684: @subsection Other system documentation 2685: @c --------------------------------------------------------------------- 2686: 2687: @table @i 2688: 2689: @item any restrictions a multiprogramming system places on the use of buffer addresses: 2690: No restrictions (yet). 2691: 2692: @item the number of blocks available for source and data: 2693: depends on your disk space. 2694: 2695: @end table 2696: 2697: 2698: @c ===================================================================== 2699: @node The optional Double Number word set, The optional Exception word set, The optional Block word set, ANS conformance 2700: @section The optional Double Number word set 2701: @c ===================================================================== 2702: 2703: @menu 1.15 anton 2704: * double-ambcond:: Ambiguous Conditions 1.14 anton 2705: @end menu 2706: 2707: 2708: @c --------------------------------------------------------------------- 1.15 anton 2709: @node double-ambcond, , The optional Double Number word set, The optional Double Number word set 1.14 anton 2710: @subsection Ambiguous conditions 2711: @c --------------------------------------------------------------------- 2712: 2713: @table @i 2714: 1.15 anton 2715: @item @var{d} outside of range of @var{n} in @code{D>S}: 1.14 anton 2716: The least significant cell of @var{d} is produced. 2717: 2718: @end table 2719: 2720: 2721: @c ===================================================================== 2722: @node The optional Exception word set, The optional Facility word set, The optional Double Number word set, ANS conformance 2723: @section The optional Exception word set 2724: @c ===================================================================== 2725: 2726: @menu 1.15 anton 2727: * exception-idef:: Implementation Defined Options 1.14 anton 2728: @end menu 2729: 2730: 2731: @c --------------------------------------------------------------------- 1.15 anton 2732: @node exception-idef, , The optional Exception word set, The optional Exception word set 1.14 anton 2733: @subsection Implementation Defined Options 2734: @c --------------------------------------------------------------------- 2735: 2736: @table @i 2737: @item @code{THROW}-codes used in the system: 2738: The codes -256@minus{}-511 are used for reporting signals (see 2739: @file{errore.fs}). The codes -512@minus{}-2047 are used for OS errors 2740: (for file and memory allocation operations). The mapping from OS error 2741: numbers to throw code is -512@minus{}@var{errno}. One side effect of 2742: this mapping is that undefined OS errors produce a message with a 2743: strange number; e.g., @code{-1000 THROW} results in @code{Unknown error 2744: 488} on my system. 2745: @end table 2746: 2747: @c ===================================================================== 2748: @node The optional Facility word set, The optional File-Access word set, The optional Exception word set, ANS conformance 2749: @section The optional Facility word set 2750: @c ===================================================================== 2751: 2752: @menu 1.15 anton 2753: * facility-idef:: Implementation Defined Options 2754: * facility-ambcond:: Ambiguous Conditions 1.14 anton 2755: @end menu 2756: 2757: 2758: @c --------------------------------------------------------------------- 2759: @node facility-idef, facility-ambcond, The optional Facility word set, The optional Facility word set 2760: @subsection Implementation Defined Options 2761: @c --------------------------------------------------------------------- 2762: 2763: @table @i 2764: 2765: @item encoding of keyboard events (@code{EKEY}): 2766: Not yet implemeted. 2767: 2768: @item duration of a system clock tick 2769: System dependent. With respect to @code{MS}, the time is specified in 2770: microseconds. How well the OS and the hardware implement this, is 2771: another question. 2772: 2773: @item repeatability to be expected from the execution of @code{MS}: 2774: System dependent. On Unix, a lot depends on load. If the system is 1.17 anton 2775: lightly loaded, and the delay is short enough that Gforth does not get 1.14 anton 2776: swapped out, the performance should be acceptable. Under MS-DOS and 2777: other single-tasking systems, it should be good. 2778: 2779: @end table 2780: 2781: 2782: @c --------------------------------------------------------------------- 1.15 anton 2783: @node facility-ambcond, , facility-idef, The optional Facility word set 1.14 anton 2784: @subsection Ambiguous conditions 2785: @c --------------------------------------------------------------------- 2786: 2787: @table @i 2788: 2789: @item @code{AT-XY} can't be performed on user output device: 2790: Largely terminal dependant. No range checks are done on the arguments. 2791: No errors are reported. You may see some garbage appearing, you may see 2792: simply nothing happen. 2793: 2794: @end table 2795: 2796: 2797: @c ===================================================================== 2798: @node The optional File-Access word set, The optional Floating-Point word set, The optional Facility word set, ANS conformance 2799: @section The optional File-Access word set 2800: @c ===================================================================== 2801: 2802: @menu 1.15 anton 2803: * file-idef:: Implementation Defined Options 2804: * file-ambcond:: Ambiguous Conditions 1.14 anton 2805: @end menu 2806: 2807: 2808: @c --------------------------------------------------------------------- 2809: @node file-idef, file-ambcond, The optional File-Access word set, The optional File-Access word set 2810: @subsection Implementation Defined Options 2811: @c --------------------------------------------------------------------- 2812: 2813: @table @i 2814: 2815: @item File access methods used: 2816: @code{R/O}, @code{R/W} and @code{BIN} work as you would 2817: expect. @code{W/O} translates into the C file opening mode @code{w} (or 2818: @code{wb}): The file is cleared, if it exists, and created, if it does 1.15 anton 2819: not (both with @code{open-file} and @code{create-file}). Under Unix 1.14 anton 2820: @code{create-file} creates a file with 666 permissions modified by your 2821: umask. 2822: 2823: @item file exceptions: 2824: The file words do not raise exceptions (except, perhaps, memory access 2825: faults when you pass illegal addresses or file-ids). 2826: 2827: @item file line terminator: 2828: System-dependent. Gforth uses C's newline character as line 2829: terminator. What the actual character code(s) of this are is 2830: system-dependent. 2831: 2832: @item file name format 2833: System dependent. Gforth just uses the file name format of your OS. 2834: 2835: @item information returned by @code{FILE-STATUS}: 2836: @code{FILE-STATUS} returns the most powerful file access mode allowed 2837: for the file: Either @code{R/O}, @code{W/O} or @code{R/W}. If the file 2838: cannot be accessed, @code{R/O BIN} is returned. @code{BIN} is applicable 2839: along with the retured mode. 2840: 2841: @item input file state after an exception when including source: 2842: All files that are left via the exception are closed. 2843: 2844: @item @var{ior} values and meaning: 1.15 anton 2845: The @var{ior}s returned by the file and memory allocation words are 2846: intended as throw codes. They typically are in the range 2847: -512@minus{}-2047 of OS errors. The mapping from OS error numbers to 2848: @var{ior}s is -512@minus{}@var{errno}. 1.14 anton 2849: 2850: @item maximum depth of file input nesting: 2851: limited by the amount of return stack, locals/TIB stack, and the number 2852: of open files available. This should not give you troubles. 2853: 2854: @item maximum size of input line: 2855: @code{/line}. Currently 255. 2856: 2857: @item methods of mapping block ranges to files: 2858: Currently, the block words automatically access the file 2859: @file{blocks.fb} in the currend working directory. More sophisticated 2860: methods could be implemented if there is demand (and a volunteer). 2861: 2862: @item number of string buffers provided by @code{S"}: 2863: 1 2864: 2865: @item size of string buffer used by @code{S"}: 2866: @code{/line}. currently 255. 2867: 2868: @end table 2869: 2870: @c --------------------------------------------------------------------- 1.15 anton 2871: @node file-ambcond, , file-idef, The optional File-Access word set 1.14 anton 2872: @subsection Ambiguous conditions 2873: @c --------------------------------------------------------------------- 2874: 2875: @table @i 2876: 2877: @item attempting to position a file outside it's boundaries: 2878: @code{REPOSITION-FILE} is performed as usual: Afterwards, 2879: @code{FILE-POSITION} returns the value given to @code{REPOSITION-FILE}. 2880: 2881: @item attempting to read from file positions not yet written: 2882: End-of-file, i.e., zero characters are read and no error is reported. 2883: 2884: @item @var{file-id} is invalid (@code{INCLUDE-FILE}): 2885: An appropriate exception may be thrown, but a memory fault or other 2886: problem is more probable. 2887: 2888: @item I/O exception reading or closing @var{file-id} (@code{include-file}, @code{included}): 2889: The @var{ior} produced by the operation, that discovered the problem, is 2890: thrown. 2891: 2892: @item named file cannot be opened (@code{included}): 2893: The @var{ior} produced by @code{open-file} is thrown. 2894: 2895: @item requesting an unmapped block number: 2896: There are no unmapped legal block numbers. On some operating systems, 2897: writing a block with a large number may overflow the file system and 2898: have an error message as consequence. 2899: 2900: @item using @code{source-id} when @code{blk} is non-zero: 2901: @code{source-id} performs its function. Typically it will give the id of 2902: the source which loaded the block. (Better ideas?) 2903: 2904: @end table 2905: 2906: 2907: @c ===================================================================== 2908: @node The optional Floating-Point word set, The optional Locals word set, The optional File-Access word set, ANS conformance 1.15 anton 2909: @section The optional Floating-Point word set 1.14 anton 2910: @c ===================================================================== 2911: 2912: @menu 1.15 anton 2913: * floating-idef:: Implementation Defined Options 2914: * floating-ambcond:: Ambiguous Conditions 1.14 anton 2915: @end menu 2916: 2917: 2918: @c --------------------------------------------------------------------- 2919: @node floating-idef, floating-ambcond, The optional Floating-Point word set, The optional Floating-Point word set 2920: @subsection Implementation Defined Options 2921: @c --------------------------------------------------------------------- 2922: 2923: @table @i 2924: 1.15 anton 2925: @item format and range of floating point numbers: 2926: System-dependent; the @code{double} type of C. 1.14 anton 2927: 1.15 anton 2928: @item results of @code{REPRESENT} when @var{float} is out of range: 2929: System dependent; @code{REPRESENT} is implemented using the C library 2930: function @code{ecvt()} and inherits its behaviour in this respect. 1.14 anton 2931: 1.15 anton 2932: @item rounding or truncation of floating-point numbers: 2933: What's the question?!! 1.14 anton 2934: 1.15 anton 2935: @item size of floating-point stack: 2936: @code{s" FLOATING-STACK" environment? drop .}. Can be changed at startup 2937: with the command-line option @code{-f}. 1.14 anton 2938: 1.15 anton 2939: @item width of floating-point stack: 2940: @code{1 floats}. 1.14 anton 2941: 2942: @end table 2943: 2944: 2945: @c --------------------------------------------------------------------- 1.15 anton 2946: @node floating-ambcond, , floating-idef, The optional Floating-Point word set 2947: @subsection Ambiguous conditions 1.14 anton 2948: @c --------------------------------------------------------------------- 2949: 2950: @table @i 2951: 1.15 anton 2952: @item @code{df@@} or @code{df!} used with an address that is not double-float aligned: 2953: System-dependent. Typically results in an alignment fault like other 2954: alignment violations. 1.14 anton 2955: 1.15 anton 2956: @item @code{f@@} or @code{f!} used with an address that is not float aligned: 2957: System-dependent. Typically results in an alignment fault like other 2958: alignment violations. 1.14 anton 2959: 1.15 anton 2960: @item Floating-point result out of range: 2961: System-dependent. Can result in a @code{-55 THROW} (Floating-point 2962: unidentified fault), or can produce a special value representing, e.g., 2963: Infinity. 1.14 anton 2964: 1.15 anton 2965: @item @code{sf@@} or @code{sf!} used with an address that is not single-float aligned: 2966: System-dependent. Typically results in an alignment fault like other 2967: alignment violations. 1.14 anton 2968: 1.15 anton 2969: @item BASE is not decimal (@code{REPRESENT}, @code{F.}, @code{FE.}, @code{FS.}): 2970: The floating-point number is converted into decimal nonetheless. 1.14 anton 2971: 1.15 anton 2972: @item Both arguments are equal to zero (@code{FATAN2}): 2973: System-dependent. @code{FATAN2} is implemented using the C library 2974: function @code{atan2()}. 1.14 anton 2975: 1.15 anton 2976: @item Using ftan on an argument @var{r1} where cos(@var{r1}) is zero: 2977: System-dependent. Anyway, typically the cos of @var{r1} will not be zero 2978: because of small errors and the tan will be a very large (or very small) 2979: but finite number. 1.14 anton 2980: 1.15 anton 2981: @item @var{d} cannot be presented precisely as a float in @code{D>F}: 2982: The result is rounded to the nearest float. 1.14 anton 2983: 1.15 anton 2984: @item dividing by zero: 2985: @code{-55 throw} (Floating-point unidentified fault) 1.14 anton 2986: 1.15 anton 2987: @item exponent too big for conversion (@code{DF!}, @code{DF@@}, @code{SF!}, @code{SF@@}): 2988: System dependent. On IEEE-FP based systems the number is converted into 2989: an infinity. 1.14 anton 2990: 1.15 anton 2991: @item @var{float}<1 (@code{facosh}): 2992: @code{-55 throw} (Floating-point unidentified fault) 1.14 anton 2993: 1.15 anton 2994: @item @var{float}=<-1 (@code{flnp1}): 2995: @code{-55 throw} (Floating-point unidentified fault). On IEEE-FP systems 2996: negative infinity is typically produced for @var{float}=-1. 1.14 anton 2997: 1.15 anton 2998: @item @var{float}=<0 (@code{fln}, @code{flog}): 2999: @code{-55 throw} (Floating-point unidentified fault). On IEEE-FP systems 3000: negative infinity is typically produced for @var{float}=0. 1.14 anton 3001: 1.15 anton 3002: @item @var{float}<0 (@code{fasinh}, @code{fsqrt}): 3003: @code{-55 throw} (Floating-point unidentified fault). @code{fasinh} 3004: produces values for these inputs on my Linux box (Bug in the C library?) 1.14 anton 3005: 1.15 anton 3006: @item |@var{float}|>1 (@code{facos}, @code{fasin}, @code{fatanh}): 3007: @code{-55 throw} (Floating-point unidentified fault). 1.14 anton 3008: 1.15 anton 3009: @item integer part of float cannot be represented by @var{d} in @code{f>d}: 3010: @code{-55 throw} (Floating-point unidentified fault). 1.14 anton 3011: 1.15 anton 3012: @item string larger than pictured numeric output area (@code{f.}, @code{fe.}, @code{fs.}): 3013: This does not happen. 3014: @end table 1.14 anton 3015: 3016: 3017: 3018: @c ===================================================================== 1.15 anton 3019: @node The optional Locals word set, The optional Memory-Allocation word set, The optional Floating-Point word set, ANS conformance 3020: @section The optional Locals word set 1.14 anton 3021: @c ===================================================================== 3022: 3023: @menu 1.15 anton 3024: * locals-idef:: Implementation Defined Options 3025: * locals-ambcond:: Ambiguous Conditions 1.14 anton 3026: @end menu 3027: 3028: 3029: @c --------------------------------------------------------------------- 1.15 anton 3030: @node locals-idef, locals-ambcond, The optional Locals word set, The optional Locals word set 1.14 anton 3031: @subsection Implementation Defined Options 3032: @c --------------------------------------------------------------------- 3033: 3034: @table @i 3035: 1.15 anton 3036: @item maximum number of locals in a definition: 3037: @code{s" #locals" environment? drop .}. Currently 15. This is a lower 3038: bound, e.g., on a 32-bit machine there can be 41 locals of up to 8 3039: characters. The number of locals in a definition is bounded by the size 3040: of locals-buffer, which contains the names of the locals. 1.14 anton 3041: 3042: @end table 3043: 3044: 3045: @c --------------------------------------------------------------------- 1.15 anton 3046: @node locals-ambcond, , locals-idef, The optional Locals word set 1.14 anton 3047: @subsection Ambiguous conditions 3048: @c --------------------------------------------------------------------- 3049: 3050: @table @i 3051: 1.15 anton 3052: @item executing a named local in interpretation state: 3053: @code{-14 throw} (Interpreting a compile-only word). 1.14 anton 3054: 1.15 anton 3055: @item @var{name} not defined by @code{VALUE} or @code{(LOCAL)} (@code{TO}): 3056: @code{-32 throw} (Invalid name argument) 1.14 anton 3057: 3058: @end table 3059: 3060: 3061: @c ===================================================================== 1.15 anton 3062: @node The optional Memory-Allocation word set, The optional Programming-Tools word set, The optional Locals word set, ANS conformance 3063: @section The optional Memory-Allocation word set 1.14 anton 3064: @c ===================================================================== 3065: 3066: @menu 1.15 anton 3067: * memory-idef:: Implementation Defined Options 1.14 anton 3068: @end menu 3069: 3070: 3071: @c --------------------------------------------------------------------- 1.15 anton 3072: @node memory-idef, , The optional Memory-Allocation word set, The optional Memory-Allocation word set 1.14 anton 3073: @subsection Implementation Defined Options 3074: @c --------------------------------------------------------------------- 3075: 3076: @table @i 3077: 1.15 anton 3078: @item values and meaning of @var{ior}: 3079: The @var{ior}s returned by the file and memory allocation words are 3080: intended as throw codes. They typically are in the range 3081: -512@minus{}-2047 of OS errors. The mapping from OS error numbers to 3082: @var{ior}s is -512@minus{}@var{errno}. 1.14 anton 3083: 3084: @end table 3085: 3086: @c ===================================================================== 1.15 anton 3087: @node The optional Programming-Tools word set, The optional Search-Order word set, The optional Memory-Allocation word set, ANS conformance 3088: @section The optional Programming-Tools word set 1.14 anton 3089: @c ===================================================================== 3090: 3091: @menu 1.15 anton 3092: * programming-idef:: Implementation Defined Options 3093: * programming-ambcond:: Ambiguous Conditions 1.14 anton 3094: @end menu 3095: 3096: 3097: @c --------------------------------------------------------------------- 1.15 anton 3098: @node programming-idef, programming-ambcond, The optional Programming-Tools word set, The optional Programming-Tools word set 1.14 anton 3099: @subsection Implementation Defined Options 3100: @c --------------------------------------------------------------------- 3101: 3102: @table @i 3103: 1.15 anton 3104: @item ending sequence for input following @code{;code} and @code{code}: 3105: Not implemented (yet). 1.14 anton 3106: 1.15 anton 3107: @item manner of processing input following @code{;code} and @code{code}: 3108: Not implemented (yet). 3109: 3110: @item search order capability for @code{EDITOR} and @code{ASSEMBLER}: 3111: Not implemented (yet). If they were implemented, they would use the 3112: search order wordset. 3113: 3114: @item source and format of display by @code{SEE}: 3115: The source for @code{see} is the intermediate code used by the inner 3116: interpreter. The current @code{see} tries to output Forth source code 3117: as well as possible. 3118: 1.14 anton 3119: @end table 3120: 3121: @c --------------------------------------------------------------------- 1.15 anton 3122: @node programming-ambcond, , programming-idef, The optional Programming-Tools word set 1.14 anton 3123: @subsection Ambiguous conditions 3124: @c --------------------------------------------------------------------- 3125: 3126: @table @i 3127: 1.15 anton 3128: @item deleting the compilation wordlist (@code{FORGET}): 3129: Not implemented (yet). 1.14 anton 3130: 1.15 anton 3131: @item fewer than @var{u}+1 items on the control flow stack (@code{CS-PICK}, @code{CS-ROLL}): 3132: This typically results in an @code{abort"} with a descriptive error 3133: message (may change into a @code{-22 throw} (Control structure mismatch) 3134: in the future). You may also get a memory access error. If you are 3135: unlucky, this ambiguous condition is not caught. 3136: 3137: @item @var{name} can't be found (@code{forget}): 3138: Not implemented (yet). 1.14 anton 3139: 1.15 anton 3140: @item @var{name} not defined via @code{CREATE}: 3141: @code{;code} is not implemented (yet). If it were, it would behave like 3142: @code{DOES>} in this respect, i.e., change the execution semantics of 3143: the last defined word no matter how it was defined. 1.14 anton 3144: 1.15 anton 3145: @item @code{POSTPONE} applied to @code{[IF]}: 3146: After defining @code{: X POSTPONE [IF] ; IMMEDIATE}. @code{X} is 3147: equivalent to @code{[IF]}. 1.14 anton 3148: 1.15 anton 3149: @item reaching the end of the input source before matching @code{[ELSE]} or @code{[THEN]}: 3150: Continue in the same state of conditional compilation in the next outer 3151: input source. Currently there is no warning to the user about this. 1.14 anton 3152: 1.15 anton 3153: @item removing a needed definition (@code{FORGET}): 3154: Not implemented (yet). 1.14 anton 3155: 3156: @end table 3157: 3158: 3159: @c ===================================================================== 1.15 anton 3160: @node The optional Search-Order word set, , The optional Programming-Tools word set, ANS conformance 3161: @section The optional Search-Order word set 1.14 anton 3162: @c ===================================================================== 3163: 3164: @menu 1.15 anton 3165: * search-idef:: Implementation Defined Options 3166: * search-ambcond:: Ambiguous Conditions 1.14 anton 3167: @end menu 3168: 3169: 3170: @c --------------------------------------------------------------------- 1.15 anton 3171: @node search-idef, search-ambcond, The optional Search-Order word set, The optional Search-Order word set 1.14 anton 3172: @subsection Implementation Defined Options 3173: @c --------------------------------------------------------------------- 3174: 3175: @table @i 3176: 1.15 anton 3177: @item maximum number of word lists in search order: 3178: @code{s" wordlists" environment? drop .}. Currently 16. 3179: 3180: @item minimum search order: 3181: @code{root root}. 1.14 anton 3182: 3183: @end table 3184: 3185: @c --------------------------------------------------------------------- 1.15 anton 3186: @node search-ambcond, , search-idef, The optional Search-Order word set 1.14 anton 3187: @subsection Ambiguous conditions 3188: @c --------------------------------------------------------------------- 3189: 3190: @table @i 3191: 1.15 anton 3192: @item changing the compilation wordlist (during compilation): 3193: The definition is put into the wordlist that is the compilation wordlist 3194: when @code{REVEAL} is executed (by @code{;}, @code{DOES>}, 3195: @code{RECURSIVE}, etc.). 1.14 anton 3196: 1.15 anton 3197: @item search order empty (@code{previous}): 3198: @code{abort" Vocstack empty"}. 1.14 anton 3199: 1.15 anton 3200: @item too many word lists in search order (@code{also}): 3201: @code{abort" Vocstack full"}. 1.14 anton 3202: 3203: @end table 1.13 anton 3204: 3205: 1.17 anton 3206: @node Model, Emacs and Gforth, ANS conformance, Top 1.4 anton 3207: @chapter Model 3208: 1.17 anton 3209: @node Emacs and Gforth, Internals, Model, Top 3210: @chapter Emacs and Gforth 1.4 anton 3211: 1.17 anton 3212: Gforth comes with @file{gforth.el}, an improved version of 1.4 anton 3213: @file{forth.el} by Goran Rydqvist (icluded in the TILE package). The 3214: improvements are a better (but still not perfect) handling of 3215: indentation. I have also added comment paragraph filling (@kbd{M-q}), 1.8 anton 3216: commenting (@kbd{C-x \}) and uncommenting (@kbd{C-u C-x \}) regions and 3217: removing debugging tracers (@kbd{C-x ~}, @pxref{Debugging}). I left the 3218: stuff I do not use alone, even though some of it only makes sense for 3219: TILE. To get a description of these features, enter Forth mode and type 3220: @kbd{C-h m}. 1.4 anton 3221: 1.17 anton 3222: In addition, Gforth supports Emacs quite well: The source code locations 1.4 anton 3223: given in error messages, debugging output (from @code{~~}) and failed 3224: assertion messages are in the right format for Emacs' compilation mode 3225: (@pxref{Compilation, , Running Compilations under Emacs, emacs, Emacs 3226: Manual}) so the source location corresponding to an error or other 3227: message is only a few keystrokes away (@kbd{C-x `} for the next error, 3228: @kbd{C-c C-c} for the error under the cursor). 3229: 3230: Also, if you @code{include} @file{etags.fs}, a new @file{TAGS} file 3231: (@pxref{Tags, , Tags Tables, emacs, Emacs Manual}) will be produced that 3232: contains the definitions of all words defined afterwards. You can then 3233: find the source for a word using @kbd{M-.}. Note that emacs can use 1.17 anton 3234: several tags files at the same time (e.g., one for the Gforth sources 1.4 anton 3235: and one for your program). 3236: 3237: To get all these benefits, add the following lines to your @file{.emacs} 3238: file: 3239: 3240: @example 3241: (autoload 'forth-mode "gforth.el") 3242: (setq auto-mode-alist (cons '("\\.fs\\'" . forth-mode) auto-mode-alist)) 3243: @end example 3244: 1.17 anton 3245: @node Internals, Bugs, Emacs and Gforth, Top 1.3 anton 3246: @chapter Internals 3247: 1.17 anton 3248: Reading this section is not necessary for programming with Gforth. It 3249: should be helpful for finding your way in the Gforth sources. 1.3 anton 3250: 1.24 anton 3251: The ideas in this section have also been published in the papers 3252: @cite{ANS fig/GNU/??? Forth} (in German) by Bernd Paysan, presented at 3253: the Forth-Tagung '93 and @cite{A Portable Forth Engine} by M. Anton 3254: Ertl, presented at EuroForth '93; the latter is available at 3255: @*@file{}. 3256: 1.4 anton 3257: @menu 3258: * Portability:: 3259: * Threading:: 3260: * Primitives:: 3261: * System Architecture:: 1.17 anton 3262: * Performance:: 1.4 anton 3263: @end menu 3264: 3265: @node Portability, Threading, Internals, Internals 1.3 anton 3266: @section Portability 3267: 3268: One of the main goals of the effort is availability across a wide range 3269: of personal machines. fig-Forth, and, to a lesser extent, F83, achieved 3270: this goal by manually coding the engine in assembly language for several 3271: then-popular processors. This approach is very labor-intensive and the 3272: results are short-lived due to progress in computer architecture. 3273: 3274: Others have avoided this problem by coding in C, e.g., Mitch Bradley 3275: (cforth), Mikael Patel (TILE) and Dirk Zoller (pfe). This approach is 3276: particularly popular for UNIX-based Forths due to the large variety of 3277: architectures of UNIX machines. Unfortunately an implementation in C 3278: does not mix well with the goals of efficiency and with using 3279: traditional techniques: Indirect or direct threading cannot be expressed 3280: in C, and switch threading, the fastest technique available in C, is 3281: significantly slower. Another problem with C is that it's very 3282: cumbersome to express double integer arithmetic. 3283: 3284: Fortunately, there is a portable language that does not have these 3285: limitations: GNU C, the version of C processed by the GNU C compiler 3286: (@pxref{C Extensions, , Extensions to the C Language Family, gcc.info, 3287: GNU C Manual}). Its labels as values feature (@pxref{Labels as Values, , 3288: Labels as Values, gcc.info, GNU C Manual}) makes direct and indirect 3289: threading possible, its @code{long long} type (@pxref{Long Long, , 3290: Double-Word Integers, gcc.info, GNU C Manual}) corresponds to Forths 3291: double numbers. GNU C is available for free on all important (and many 3292: unimportant) UNIX machines, VMS, 80386s running MS-DOS, the Amiga, and 3293: the Atari ST, so a Forth written in GNU C can run on all these 1.17 anton 3294: machines. 1.3 anton 3295: 3296: Writing in a portable language has the reputation of producing code that 3297: is slower than assembly. For our Forth engine we repeatedly looked at 3298: the code produced by the compiler and eliminated most compiler-induced 3299: inefficiencies by appropriate changes in the source-code. 3300: 3301: However, register allocation cannot be portably influenced by the 3302: programmer, leading to some inefficiencies on register-starved 3303: machines. We use explicit register declarations (@pxref{Explicit Reg 3304: Vars, , Variables in Specified Registers, gcc.info, GNU C Manual}) to 3305: improve the speed on some machines. They are turned on by using the 3306: @code{gcc} switch @code{-DFORCE_REG}. Unfortunately, this feature not 3307: only depends on the machine, but also on the compiler version: On some 3308: machines some compiler versions produce incorrect code when certain 3309: explicit register declarations are used. So by default 3310: @code{-DFORCE_REG} is not used. 3311: 1.4 anton 3312: @node Threading, Primitives, Portability, Internals 1.3 anton 3313: @section Threading 3314: 3315: GNU C's labels as values extension (available since @code{gcc-2.0}, 3316: @pxref{Labels as Values, , Labels as Values, gcc.info, GNU C Manual}) 3317: makes it possible to take the address of @var{label} by writing 3318: @code{&&@var{label}}. This address can then be used in a statement like 3319: @code{goto *@var{address}}. I.e., @code{goto *&&x} is the same as 3320: @code{goto x}. 3321: 3322: With this feature an indirect threaded NEXT looks like: 3323: @example 3324: cfa = *ip++; 3325: ca = *cfa; 3326: goto *ca; 3327: @end example 3328: For those unfamiliar with the names: @code{ip} is the Forth instruction 3329: pointer; the @code{cfa} (code-field address) corresponds to ANS Forths 3330: execution token and points to the code field of the next word to be 3331: executed; The @code{ca} (code address) fetched from there points to some 3332: executable code, e.g., a primitive or the colon definition handler 3333: @code{docol}. 3334: 3335: Direct threading is even simpler: 3336: @example 3337: ca = *ip++; 3338: goto *ca; 3339: @end example 3340: 3341: Of course we have packaged the whole thing neatly in macros called 3342: @code{NEXT} and @code{NEXT1} (the part of NEXT after fetching the cfa). 3343: 1.4 anton 3344: @menu 3345: * Scheduling:: 3346: * Direct or Indirect Threaded?:: 3347: * DOES>:: 3348: @end menu 3349: 3350: @node Scheduling, Direct or Indirect Threaded?, Threading, Threading 1.3 anton 3351: @subsection Scheduling 3352: 3353: There is a little complication: Pipelined and superscalar processors, 3354: i.e., RISC and some modern CISC machines can process independent 3355: instructions while waiting for the results of an instruction. The 3356: compiler usually reorders (schedules) the instructions in a way that 3357: achieves good usage of these delay slots. However, on our first tries 3358: the compiler did not do well on scheduling primitives. E.g., for 3359: @code{+} implemented as 3360: @example 3361: n=sp[0]+sp[1]; 3362: sp++; 3363: sp[0]=n; 3364: NEXT; 3365: @end example 3366: the NEXT comes strictly after the other code, i.e., there is nearly no 3367: scheduling. After a little thought the problem becomes clear: The 3368: compiler cannot know that sp and ip point to different addresses (and 1.4 anton 3369: the version of @code{gcc} we used would not know it even if it was 3370: possible), so it could not move the load of the cfa above the store to 3371: the TOS. Indeed the pointers could be the same, if code on or very near 3372: the top of stack were executed. In the interest of speed we chose to 3373: forbid this probably unused ``feature'' and helped the compiler in 3374: scheduling: NEXT is divided into the loading part (@code{NEXT_P1}) and 3375: the goto part (@code{NEXT_P2}). @code{+} now looks like: 1.3 anton 3376: @example 3377: n=sp[0]+sp[1]; 3378: sp++; 3379: NEXT_P1; 3380: sp[0]=n; 3381: NEXT_P2; 3382: @end example 1.4 anton 3383: This can be scheduled optimally by the compiler. 1.3 anton 3384: 3385: This division can be turned off with the switch @code{-DCISC_NEXT}. This 3386: switch is on by default on machines that do not profit from scheduling 3387: (e.g., the 80386), in order to preserve registers. 3388: 1.4 anton 3389: @node Direct or Indirect Threaded?, DOES>, Scheduling, Threading 1.3 anton 3390: @subsection Direct or Indirect Threaded? 3391: 3392: Both! After packaging the nasty details in macro definitions we 3393: realized that we could switch between direct and indirect threading by 3394: simply setting a compilation flag (@code{-DDIRECT_THREADED}) and 3395: defining a few machine-specific macros for the direct-threading case. 3396: On the Forth level we also offer access words that hide the 3397: differences between the threading methods (@pxref{Threading Words}). 3398: 3399: Indirect threading is implemented completely 3400: machine-independently. Direct threading needs routines for creating 3401: jumps to the executable code (e.g. to docol or dodoes). These routines 3402: are inherently machine-dependent, but they do not amount to many source 3403: lines. I.e., even porting direct threading to a new machine is a small 3404: effort. 3405: 1.4 anton 3406: @node DOES>, , Direct or Indirect Threaded?, Threading 1.3 anton 3407: @subsection DOES> 3408: One of the most complex parts of a Forth engine is @code{dodoes}, i.e., 3409: the chunk of code executed by every word defined by a 3410: @code{CREATE}...@code{DOES>} pair. The main problem here is: How to find 3411: the Forth code to be executed, i.e. the code after the @code{DOES>} (the 3412: DOES-code)? There are two solutions: 3413: 3414: In fig-Forth the code field points directly to the dodoes and the 3415: DOES-code address is stored in the cell after the code address 3416: (i.e. at cfa cell+). It may seem that this solution is illegal in the 3417: Forth-79 and all later standards, because in fig-Forth this address 3418: lies in the body (which is illegal in these standards). However, by 3419: making the code field larger for all words this solution becomes legal 3420: again. We use this approach for the indirect threaded version. Leaving 3421: a cell unused in most words is a bit wasteful, but on the machines we 3422: are targetting this is hardly a problem. The other reason for having a 3423: code field size of two cells is to avoid having different image files 1.4 anton 3424: for direct and indirect threaded systems (@pxref{System Architecture}). 1.3 anton 3425: 3426: The other approach is that the code field points or jumps to the cell 3427: after @code{DOES}. In this variant there is a jump to @code{dodoes} at 3428: this address. @code{dodoes} can then get the DOES-code address by 3429: computing the code address, i.e., the address of the jump to dodoes, 3430: and add the length of that jump field. A variant of this is to have a 3431: call to @code{dodoes} after the @code{DOES>}; then the return address 3432: (which can be found in the return register on RISCs) is the DOES-code 3433: address. Since the two cells available in the code field are usually 3434: used up by the jump to the code address in direct threading, we use 3435: this approach for direct threading. We did not want to add another 3436: cell to the code field. 3437: 1.4 anton 3438: @node Primitives, System Architecture, Threading, Internals 1.3 anton 3439: @section Primitives 3440: 1.4 anton 3441: @menu 3442: * Automatic Generation:: 3443: * TOS Optimization:: 3444: * Produced code:: 3445: @end menu 3446: 3447: @node Automatic Generation, TOS Optimization, Primitives, Primitives 1.3 anton 3448: @subsection Automatic Generation 3449: 3450: Since the primitives are implemented in a portable language, there is no 3451: longer any need to minimize the number of primitives. On the contrary, 3452: having many primitives is an advantage: speed. In order to reduce the 3453: number of errors in primitives and to make programming them easier, we 3454: provide a tool, the primitive generator (@file{prims2x.fs}), that 3455: automatically generates most (and sometimes all) of the C code for a 3456: primitive from the stack effect notation. The source for a primitive 3457: has the following form: 3458: 3459: @format 3460: @var{Forth-name} @var{stack-effect} @var{category} [@var{pronounc.}] 3461: [@code{""}@var{glossary entry}@code{""}] 3462: @var{C code} 3463: [@code{:} 3464: @var{Forth code}] 3465: @end format 3466: 3467: The items in brackets are optional. The category and glossary fields 3468: are there for generating the documentation, the Forth code is there 3469: for manual implementations on machines without GNU C. E.g., the source 3470: for the primitive @code{+} is: 3471: @example 3472: + n1 n2 -- n core plus 3473: n = n1+n2; 3474: @end example 3475: 3476: This looks like a specification, but in fact @code{n = n1+n2} is C 3477: code. Our primitive generation tool extracts a lot of information from 3478: the stack effect notations@footnote{We use a one-stack notation, even 3479: though we have separate data and floating-point stacks; The separate 3480: notation can be generated easily from the unified notation.}: The number 3481: of items popped from and pushed on the stack, their type, and by what 3482: name they are referred to in the C code. It then generates a C code 3483: prelude and postlude for each primitive. The final C code for @code{+} 3484: looks like this: 3485: 3486: @example 3487: I_plus: /* + ( n1 n2 -- n ) */ /* label, stack effect */ 3488: /* */ /* documentation */ 1.4 anton 3489: @{ 1.3 anton 3490: DEF_CA /* definition of variable ca (indirect threading) */ 3491: Cell n1; /* definitions of variables */ 3492: Cell n2; 3493: Cell n; 3494: n1 = (Cell) sp[1]; /* input */ 3495: n2 = (Cell) TOS; 3496: sp += 1; /* stack adjustment */ 3497: NAME("+") /* debugging output (with -DDEBUG) */ 1.4 anton 3498: @{ 1.3 anton 3499: n = n1+n2; /* C code taken from the source */ 1.4 anton 3500: @} 1.3 anton 3501: NEXT_P1; /* NEXT part 1 */ 3502: TOS = (Cell)n; /* output */ 3503: NEXT_P2; /* NEXT part 2 */ 1.4 anton 3504: @} 1.3 anton 3505: @end example 3506: 3507: This looks long and inefficient, but the GNU C compiler optimizes quite 3508: well and produces optimal code for @code{+} on, e.g., the R3000 and the 3509: HP RISC machines: Defining the @code{n}s does not produce any code, and 3510: using them as intermediate storage also adds no cost. 3511: 3512: There are also other optimizations, that are not illustrated by this 3513: example: Assignments between simple variables are usually for free (copy 3514: propagation). If one of the stack items is not used by the primitive 3515: (e.g. in @code{drop}), the compiler eliminates the load from the stack 3516: (dead code elimination). On the other hand, there are some things that 3517: the compiler does not do, therefore they are performed by 3518: @file{prims2x.fs}: The compiler does not optimize code away that stores 3519: a stack item to the place where it just came from (e.g., @code{over}). 3520: 3521: While programming a primitive is usually easy, there are a few cases 3522: where the programmer has to take the actions of the generator into 3523: account, most notably @code{?dup}, but also words that do not (always) 3524: fall through to NEXT. 3525: 1.4 anton 3526: @node TOS Optimization, Produced code, Automatic Generation, Primitives 1.3 anton 3527: @subsection TOS Optimization 3528: 3529: An important optimization for stack machine emulators, e.g., Forth 3530: engines, is keeping one or more of the top stack items in 1.4 anton 3531: registers. If a word has the stack effect @var{in1}...@var{inx} @code{--} 3532: @var{out1}...@var{outy}, keeping the top @var{n} items in registers 1.3 anton 3533: @itemize 3534: @item 3535: is better than keeping @var{n-1} items, if @var{x>=n} and @var{y>=n}, 3536: due to fewer loads from and stores to the stack. 3537: @item is slower than keeping @var{n-1} items, if @var{x<>y} and @var{x<n} and 3538: @var{y<n}, due to additional moves between registers. 3539: @end itemize 3540: 3541: In particular, keeping one item in a register is never a disadvantage, 3542: if there are enough registers. Keeping two items in registers is a 3543: disadvantage for frequent words like @code{?branch}, constants, 3544: variables, literals and @code{i}. Therefore our generator only produces 3545: code that keeps zero or one items in registers. The generated C code 3546: covers both cases; the selection between these alternatives is made at 3547: C-compile time using the switch @code{-DUSE_TOS}. @code{TOS} in the C 3548: code for @code{+} is just a simple variable name in the one-item case, 3549: otherwise it is a macro that expands into @code{sp[0]}. Note that the 3550: GNU C compiler tries to keep simple variables like @code{TOS} in 3551: registers, and it usually succeeds, if there are enough registers. 3552: 3553: The primitive generator performs the TOS optimization for the 3554: floating-point stack, too (@code{-DUSE_FTOS}). For floating-point 3555: operations the benefit of this optimization is even larger: 3556: floating-point operations take quite long on most processors, but can be 3557: performed in parallel with other operations as long as their results are 3558: not used. If the FP-TOS is kept in a register, this works. If 3559: it is kept on the stack, i.e., in memory, the store into memory has to 3560: wait for the result of the floating-point operation, lengthening the 3561: execution time of the primitive considerably. 3562: 3563: The TOS optimization makes the automatic generation of primitives a 3564: bit more complicated. Just replacing all occurrences of @code{sp[0]} by 3565: @code{TOS} is not sufficient. There are some special cases to 3566: consider: 3567: @itemize 3568: @item In the case of @code{dup ( w -- w w )} the generator must not 3569: eliminate the store to the original location of the item on the stack, 3570: if the TOS optimization is turned on. 1.4 anton 3571: @item Primitives with stack effects of the form @code{--} 3572: @var{out1}...@var{outy} must store the TOS to the stack at the start. 3573: Likewise, primitives with the stack effect @var{in1}...@var{inx} @code{--} 1.3 anton 3574: must load the TOS from the stack at the end. But for the null stack 3575: effect @code{--} no stores or loads should be generated. 3576: @end itemize 3577: 1.4 anton 3578: @node Produced code, , TOS Optimization, Primitives 1.3 anton 3579: @subsection Produced code 3580: 3581: To see what assembly code is produced for the primitives on your machine 3582: with your compiler and your flag settings, type @code{make engine.s} and 1.4 anton 3583: look at the resulting file @file{engine.s}. 1.3 anton 3584: 1.17 anton 3585: @node System Architecture, Performance, Primitives, Internals 1.3 anton 3586: @section System Architecture 3587: 3588: Our Forth system consists not only of primitives, but also of 3589: definitions written in Forth. Since the Forth compiler itself belongs 3590: to those definitions, it is not possible to start the system with the 3591: primitives and the Forth source alone. Therefore we provide the Forth 3592: code as an image file in nearly executable form. At the start of the 3593: system a C routine loads the image file into memory, sets up the 3594: memory (stacks etc.) according to information in the image file, and 3595: starts executing Forth code. 3596: 3597: The image file format is a compromise between the goals of making it 3598: easy to generate image files and making them portable. The easiest way 3599: to generate an image file is to just generate a memory dump. However, 3600: this kind of image file cannot be used on a different machine, or on 3601: the next version of the engine on the same machine, it even might not 3602: work with the same engine compiled by a different version of the C 3603: compiler. We would like to have as few versions of the image file as 3604: possible, because we do not want to distribute many versions of the 3605: same image file, and to make it easy for the users to use their image 3606: files on many machines. We currently need to create a different image 3607: file for machines with different cell sizes and different byte order 1.17 anton 3608: (little- or big-endian)@footnote{We are considering adding information to the 1.3 anton 3609: image file that enables the loader to change the byte order.}. 3610: 3611: Forth code that is going to end up in a portable image file has to 1.4 anton 3612: comply to some restrictions: addresses have to be stored in memory with 3613: special words (@code{A!}, @code{A,}, etc.) in order to make the code 3614: relocatable. Cells, floats, etc., have to be stored at the natural 3615: alignment boundaries@footnote{E.g., store floats (8 bytes) at an address 3616: dividable by~8. This happens automatically in our system when you use 3617: the ANS Forth alignment words.}, in order to avoid alignment faults on 3618: machines with stricter alignment. The image file is produced by a 3619: metacompiler (@file{cross.fs}). 1.3 anton 3620: 3621: So, unlike the image file of Mitch Bradleys @code{cforth}, our image 3622: file is not directly executable, but has to undergo some manipulations 3623: during loading. Address relocation is performed at image load-time, not 3624: at run-time. The loader also has to replace tokens standing for 3625: primitive calls with the appropriate code-field addresses (or code 3626: addresses in the case of direct threading). 1.4 anton 3627: 1.17 anton 3628: @node Performance, , System Architecture, Internals 3629: @section Performance 3630: 3631: On RISCs the Gforth engine is very close to optimal; i.e., it is usually 3632: impossible to write a significantly faster engine. 3633: 3634: On register-starved machines like the 386 architecture processors 3635: improvements are possible, because @code{gcc} does not utilize the 3636: registers as well as a human, even with explicit register declarations; 3637: e.g., Bernd Beuster wrote a Forth system fragment in assembly language 3638: and hand-tuned it for the 486; this system is 1.19 times faster on the 3639: Sieve benchmark on a 486DX2/66 than Gforth compiled with 3640: @code{gcc-2.6.3} with @code{-DFORCE_REG}. 3641: 3642: However, this potential advantage of assembly language implementations 3643: is not necessarily realized in complete Forth systems: We compared 3644: Gforth (compiled with @code{gcc-2.6.3} and @code{-DFORCE_REG}) with 1.18 anton 3645: Win32Forth 1.2093 and LMI's NT Forth (Beta, May 1994), two systems 3646: written in assembly, and with two systems written in C: PFE-0.9.11 3647: (compiled with @code{gcc-2.6.3} with the default configuration for 3648: Linux: @code{-O2 -fomit-frame-pointer -DUSE_REGS}) and ThisForth Beta 3649: (compiled with gcc-2.6.3 -O3 -fomit-frame-pointer). We benchmarked 3650: Gforth, PFE and ThisForth on a 486DX2/66 under Linux. Kenneth O'Heskin 3651: kindly provided the results for Win32Forth and NT Forth on a 486DX2/66 3652: with similar memory performance under Windows NT. 1.17 anton 3653: 3654: We used four small benchmarks: the ubiquitous Sieve; bubble-sorting and 3655: matrix multiplication come from the Stanford integer benchmarks and have 3656: been translated into Forth by Martin Fraeman; we used the versions 3657: included in the TILE Forth package; and a recursive Fibonacci number 1.24 anton 3658: computation for benchmarking calling performance. The following table shows 1.17 anton 3659: the time taken for the benchmarks scaled by the time taken by Gforth (in 3660: other words, it shows the speedup factor that Gforth achieved over the 3661: other systems). 3662: 3663: @example 3664: relative Win32- NT This- 3665: time Gforth Forth Forth PFE Forth 3666: sieve 1.00 1.30 1.07 1.67 2.98 3667: bubble 1.00 1.30 1.40 1.66 3668: matmul 1.00 1.40 1.29 2.24 3669: fib 1.00 1.44 1.26 1.82 2.82 3670: @end example 3671: 3672: You may find the good performance of Gforth compared with the systems 3673: written in assembly language quite surprising. One important reason for 3674: the disappointing performance of these systems is probably that they are 3675: not written optimally for the 486 (e.g., they use the @code{lods} 3676: instruction). In addition, Win32Forth uses a comfortable, but costly 3677: method for relocating the Forth image: like @code{cforth}, it computes 3678: the actual addresses at run time, resulting in two address computations 3679: per NEXT (@pxref{System Architecture}). 3680: 3681: The speedup of Gforth over PFE and ThisForth can be easily explained 3682: with the self-imposed restriction to standard C (although the measured 3683: implementation of PFE uses a GNU C extension: global register 3684: variables), which makes efficient threading impossible. Moreover, 3685: current C compilers have a hard time optimizing other aspects of the 3686: ThisForth source. 3687: 3688: Note that the performance of Gforth on 386 architecture processors 3689: varies widely with the version of @code{gcc} used. E.g., @code{gcc-2.5.8} 3690: failed to allocate any of the virtual machine registers into real 3691: machine registers by itself and would not work correctly with explicit 3692: register declarations, giving a 1.3 times slower engine (on a 486DX2/66 3693: running the Sieve) than the one measured above. 3694: 1.24 anton 3695: The numbers in this section have also been published in the paper 3696: @cite{Translating Forth to Efficient C} by M. Anton Ertl and Martin 3697: Maierhofer, presented at EuroForth '95. It is available at 3698: @*@file{}; 3699: it also contains numbers for some native code systems. You can find 3700: numbers for Gforth on various machines in @file{Benchres}. 3701: 1.4 anton 3702: @node Bugs, Pedigree, Internals, Top 3703: @chapter Bugs 3704: 1.17 anton 3705: Known bugs are described in the file BUGS in the Gforth distribution. 3706: 1.24 anton 3707: If you find a bug, please send a bug report to 3708: @code{gforth-bugs@@mips.complang.tuwien.ac.at}. A bug report should 1.17 anton 3709: describe the Gforth version used (it is announced at the start of an 3710: interactive Gforth session), the machine and operating system (on Unix 3711: systems you can use @code{uname -a} to produce this information), the 1.24 anton 3712: installation options (send the @code{config.status} file), and a 3713: complete list of changes you (or your installer) have made to the Gforth 3714: sources (if any); it should contain a program (or a sequence of keyboard 3715: commands) that reproduces the bug and a description of what you think 3716: constitutes the buggy behaviour. 1.17 anton 3717: 3718: For a thorough guide on reporting bugs read @ref{Bug Reporting, , How 3719: to Report Bugs, gcc.info, GNU C Manual}. 3720: 3721: 1.4 anton 3722: @node Pedigree, Word Index, Bugs, Top 3723: @chapter Pedigree 3724: 1.17 anton 3725: Gforth descends from BigForth (1993) and fig-Forth. Gforth and PFE (by 1.24 anton 3726: Dirk Zoller) will cross-fertilize each other. Of course, a significant 3727: part of the design of Gforth was prescribed by ANS Forth. 1.17 anton 3728: 1.23 pazsan 3729: Bernd Paysan wrote BigForth, a descendent from TurboForth, an unreleased 3730: 32 bit native code version of VolksForth for the Atari ST, written 3731: mostly by Dietrich Weineck. 3732: 3733: VolksForth descends from F83. It was written by Klaus Schleisiek, Bernd 3734: Pennemann, Georg Rehfeld and Dietrich Weineck for the C64 (called 1.24 anton 3735: UltraForth there) in the mid-80s and ported to the Atari ST in 1986. 1.17 anton 3736: 1.25 ! anton 3737: Hennry Laxen and Mike Perry wrote F83 as a model implementation of the 1.17 anton 3738: Forth-83 standard. !! Pedigree? When? 3739: 3740: A team led by Bill Ragsdale implemented fig-Forth on many processors in 1.24 anton 3741: 1979. Robert Selzer and Bill Ragsdale developed the original 3742: implementation of fig-Forth for the 6502 based on microForth. 3743: 3744: The principal architect of microForth was Dean Sanderson. microForth was 3745: FORTH, Inc.'s first off-the-shelf product. It was developped in 1976 for 3746: the 1802, and subsequently implemented on the 8080, the 6800 and the 3747: Z80. 1.17 anton 3748: 1.24 anton 3749: All earlier Forth systems were custom-made, usually by Charles Moore, 3750: who discovered (as he puts it) Forth in the late 60s. 1.17 anton 3751: 3752: A part of the information in this section comes from @cite{The Evolution 3753: of Forth} by Elizabeth D. Rather, Donald R. Colburn and Charles 3754: H. Moore, presented at the HOPL-II conference and preprinted in SIGPLAN 3755: Notices 28(3), 1993. You can find more historical and genealogical 3756: information about Forth there. 3757: 1.4 anton 3758: @node Word Index, Node Index, Pedigree, Top 3759: @chapter Word Index 3760: 1.18 anton 3761: This index is as incomplete as the manual. Each word is listed with 3762: stack effect and wordset. 1.17 anton 3763: 3764: @printindex fn 3765: 1.4 anton 3766: @node Node Index, , Word Index, Top 3767: @chapter Node Index 1.17 anton 3768: 3769: This index is even less complete than the manual. 1.1 anton 3770: 3771: @contents 3772: @bye 3773: