text: /*
   * jmemmgr.c
   *
   * Copyright (C) 1991-1997, Thomas G. Lane.
   * This file is part of the Independent JPEG Group's software.
   * For conditions of distribution and use, see the accompanying README file.
   *
   * This file contains the JPEG system-independent memory management
   * routines.  This code is usable across a wide variety of machines; most
   * of the system dependencies have been isolated in a separate file.
   * The major functions provided here are:
   *   * pool-based allocation and freeing of memory;
   *   * policy decisions about how to divide available memory among the
   *     virtual arrays;
   *   * control logic for swapping virtual arrays between main memory and
   *     backing storage.
   * The separate system-dependent file provides the actual backing-storage
   * access code, and it contains the policy decision about how much total
   * main memory to use.
   * This file is system-dependent in the sense that some of its functions
   * are unnecessary in some systems.  For example, if there is enough virtual
   * memory so that backing storage will never be used, much of the virtual
   * array control logic could be removed.  (Of course, if you have that much
   * memory then you shouldn't care about a little bit of unused code...)
   */
  
  #define JPEG_INTERNALS
  #define AM_MEMORY_MANAGER	/* we define jvirt_Xarray_control structs */
  #include "jinclude.h"
  #include "jpeglib.h"
  #include "jmemsys.h"		/* import the system-dependent declarations */
  
  #ifndef NO_GETENV
  #ifndef HAVE_STDLIB_H		/* <stdlib.h> should declare getenv() */
  extern char * getenv JPP((const char * name));
  #endif
  #endif
  
  
  /*
   * Some important notes:
   *   The allocation routines provided here must never return NULL.
   *   They should exit to error_exit if unsuccessful.
   *
   *   It's not a good idea to try to merge the sarray and barray routines,
   *   even though they are textually almost the same, because samples are
   *   usually stored as bytes while coefficients are shorts or ints.  Thus,
   *   in machines where byte pointers have a different representation from
   *   word pointers, the resulting machine code could not be the same.
   */
  
  
  /*
   * Many machines require storage alignment: longs must start on 4-byte
   * boundaries, doubles on 8-byte boundaries, etc.  On such machines, malloc()
   * always returns pointers that are multiples of the worst-case alignment
   * requirement, and we had better do so too.
   * There isn't any really portable way to determine the worst-case alignment
   * requirement.  This module assumes that the alignment requirement is
   * multiples of sizeof(ALIGN_TYPE).
   * By default, we define ALIGN_TYPE as double.  This is necessary on some
   * workstations (where doubles really do need 8-byte alignment) and will work
   * fine on nearly everything.  If your machine has lesser alignment needs,
   * you can save a few bytes by making ALIGN_TYPE smaller.
   * The only place I know of where this will NOT work is certain Macintosh
   * 680x0 compilers that define double as a 10-byte IEEE extended float.
   * Doing 10-byte alignment is counterproductive because longwords won't be
   * aligned well.  Put "#define ALIGN_TYPE long" in jconfig.h if you have
   * such a compiler.
   */
  
  #ifndef ALIGN_TYPE		/* so can override from jconfig.h */
  #define ALIGN_TYPE  double
  #endif
  
  
  /*
   * We allocate objects from "pools", where each pool is gotten with a single
   * request to jpeg_get_small() or jpeg_get_large().  There is no per-object
   * overhead within a pool, except for alignment padding.  Each pool has a
   * header with a link to the next pool of the same class.
   * Small and large pool headers are identical except that the latter's
   * link pointer must be FAR on 80x86 machines.
   * Notice that the "real" header fields are union'ed with a dummy ALIGN_TYPE
   * field.  This forces the compiler to make SIZEOF(small_pool_hdr) a multiple
   * of the alignment requirement of ALIGN_TYPE.
   */
  
  typedef union small_pool_struct * small_pool_ptr;
  
  typedef union small_pool_struct {
    struct {
      small_pool_ptr next;	/* next in list of pools */
      size_t bytes_used;		/* how many bytes already used within pool */
      size_t bytes_left;		/* bytes still available in this pool */
    } hdr;
    ALIGN_TYPE dummy;		/* included in union to ensure alignment */
  } small_pool_hdr;
  
  typedef union large_pool_struct FAR * large_pool_ptr;
  
  typedef union large_pool_struct {
    struct {
      large_pool_ptr next;	/* next in list of pools */
      size_t bytes_used;		/* how many bytes already used within pool */
      size_t bytes_left;		/* bytes still available in this pool */
    } hdr;
    ALIGN_TYPE dummy;		/* included in union to ensure alignment */
  } large_pool_hdr;
  
  
  /*
   * Here is the full definition of a memory manager object.
   */
  
  typedef struct {
    struct jpeg_memory_mgr pub;	/* public fields */
  
    /* Each pool identifier (lifetime class) names a linked list of pools. */
    small_pool_ptr small_list[JPOOL_NUMPOOLS];
    large_pool_ptr large_list[JPOOL_NUMPOOLS];
  
    /* Since we only have one lifetime class of virtual arrays, only one
     * linked list is necessary (for each datatype).  Note that the virtual
     * array control blocks being linked together are actually stored somewhere
     * in the small-pool list.
     */
    jvirt_sarray_ptr virt_sarray_list;
    jvirt_barray_ptr virt_barray_list;
  
    /* This counts total space obtained from jpeg_get_small/large */
    long total_space_allocated;
  
    /* alloc_sarray and alloc_barray set this value for use by virtual
     * array routines.
     */
    JDIMENSION last_rowsperchunk;	/* from most recent alloc_sarray/barray */
  } my_memory_mgr;
  
  typedef my_memory_mgr * my_mem_ptr;
  
  
  /*
   * The control blocks for virtual arrays.
   * Note that these blocks are allocated in the "small" pool area.
   * System-dependent info for the associated backing store (if any) is hidden
   * inside the backing_store_info struct.
   */
  
  struct jvirt_sarray_control {
    JSAMPARRAY mem_buffer;	/* => the in-memory buffer */
    JDIMENSION rows_in_array;	/* total virtual array height */
    JDIMENSION samplesperrow;	/* width of array (and of memory buffer) */
    JDIMENSION maxaccess;		/* max rows accessed by access_virt_sarray */
    JDIMENSION rows_in_mem;	/* height of memory buffer */
    JDIMENSION rowsperchunk;	/* allocation chunk size in mem_buffer */
    JDIMENSION cur_start_row;	/* first logical row # in the buffer */
    JDIMENSION first_undef_row;	/* row # of first uninitialized row */
    jboolean pre_zero;		/* pre-zero mode requested? */
    jboolean dirty;		/* do current buffer contents need written? */
    jboolean b_s_open;		/* is backing-store data valid? */
    jvirt_sarray_ptr next;	/* link to next virtual sarray control block */
    backing_store_info b_s_info;	/* System-dependent control info */
  };
  
  struct jvirt_barray_control {
    JBLOCKARRAY mem_buffer;	/* => the in-memory buffer */
    JDIMENSION rows_in_array;	/* total virtual array height */
    JDIMENSION blocksperrow;	/* width of array (and of memory buffer) */
    JDIMENSION maxaccess;		/* max rows accessed by access_virt_barray */
    JDIMENSION rows_in_mem;	/* height of memory buffer */
    JDIMENSION rowsperchunk;	/* allocation chunk size in mem_buffer */
    JDIMENSION cur_start_row;	/* first logical row # in the buffer */
    JDIMENSION first_undef_row;	/* row # of first uninitialized row */
    jboolean pre_zero;		/* pre-zero mode requested? */
    jboolean dirty;		/* do current buffer contents need written? */
    jboolean b_s_open;		/* is backing-store data valid? */
    jvirt_barray_ptr next;	/* link to next virtual barray control block */
    backing_store_info b_s_info;	/* System-dependent control info */
  };
  
  
  #ifdef MEM_STATS		/* optional extra stuff for statistics */
  
  LOCAL(void)
  print_mem_stats (j_common_ptr cinfo, int pool_id)
  {
    my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
    small_pool_ptr shdr_ptr;
    large_pool_ptr lhdr_ptr;
  
    /* Since this is only a debugging stub, we can cheat a little by using
     * fprintf directly rather than going through the trace message code.
     * This is helpful because message parm array can't handle longs.
     */
    fprintf(stderr, "Freeing pool %d, total space = %ld\n",
  	  pool_id, mem->total_space_allocated);
  
    for (lhdr_ptr = mem->large_list[pool_id]; lhdr_ptr != NULL;
         lhdr_ptr = lhdr_ptr->hdr.next) {
      fprintf(stderr, "  Large chunk used %ld\n",
  	    (long) lhdr_ptr->hdr.bytes_used);
    }
  
    for (shdr_ptr = mem->small_list[pool_id]; shdr_ptr != NULL;
         shdr_ptr = shdr_ptr->hdr.next) {
      fprintf(stderr, "  Small chunk used %ld free %ld\n",
  	    (long) shdr_ptr->hdr.bytes_used,
  	    (long) shdr_ptr->hdr.bytes_left);
    }
  }
  
  #endif /* MEM_STATS */
  
  
  LOCAL(void)
  out_of_memory (j_common_ptr cinfo, int which)
  /* Report an out-of-memory error and stop execution */
  /* If we compiled MEM_STATS support, report alloc requests before dying */
  {
  #ifdef MEM_STATS
    cinfo->err->trace_level = 2;	/* force self_destruct to report stats */
  #endif
    ERREXIT1(cinfo, JERR_OUT_OF_MEMORY, which);
  }
  
  
  /*
   * Allocation of "small" objects.
   *
   * For these, we use pooled storage.  When a new pool must be created,
   * we try to get enough space for the current request plus a "slop" factor,
   * where the slop will be the amount of leftover space in the new pool.
   * The speed vs. space tradeoff is largely determined by the slop values.
   * A different slop value is provided for each pool class (lifetime),
   * and we also distinguish the first pool of a class from later ones.
   * NOTE: the values given work fairly well on both 16- and 32-bit-int
   * machines, but may be too small if longs are 64 bits or more.
   */
  
  static const size_t first_pool_slop[JPOOL_NUMPOOLS] = 
  {
  	1600,			/* first PERMANENT pool */
  	16000			/* first IMAGE pool */
  };
  
  static const size_t extra_pool_slop[JPOOL_NUMPOOLS] = 
  {
  	0,			/* additional PERMANENT pools */
  	5000			/* additional IMAGE pools */
  };
  
  #define MIN_SLOP  50		/* greater than 0 to avoid futile looping */
  
  
  METHODDEF(void *)
  alloc_small (j_common_ptr cinfo, int pool_id, size_t sizeofobject)
  /* Allocate a "small" object */
  {
    my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
    small_pool_ptr hdr_ptr, prev_hdr_ptr;
    char * data_ptr;
    size_t odd_bytes, min_request, slop;
  
    /* Check for unsatisfiable request (do now to ensure no overflow below) */
    if (sizeofobject > (size_t) (MAX_ALLOC_CHUNK-SIZEOF(small_pool_hdr)))
      out_of_memory(cinfo, 1);	/* request exceeds malloc's ability */
  
    /* Round up the requested size to a multiple of SIZEOF(ALIGN_TYPE) */
    odd_bytes = sizeofobject % SIZEOF(ALIGN_TYPE);
    if (odd_bytes > 0)
      sizeofobject += SIZEOF(ALIGN_TYPE) - odd_bytes;
  
    /* See if space is available in any existing pool */
    if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)
      ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */
    prev_hdr_ptr = NULL;
    hdr_ptr = mem->small_list[pool_id];
    while (hdr_ptr != NULL) {
      if (hdr_ptr->hdr.bytes_left >= sizeofobject)
        break;			/* found pool with enough space */
      prev_hdr_ptr = hdr_ptr;
      hdr_ptr = hdr_ptr->hdr.next;
    }
  
    /* Time to make a new pool? */
    if (hdr_ptr == NULL) {
      /* min_request is what we need now, slop is what will be leftover */
      min_request = sizeofobject + SIZEOF(small_pool_hdr);
      if (prev_hdr_ptr == NULL)	/* first pool in class? */
        slop = first_pool_slop[pool_id];
      else
        slop = extra_pool_slop[pool_id];
      /* Don't ask for more than MAX_ALLOC_CHUNK */
      if (slop > (size_t) (MAX_ALLOC_CHUNK-min_request))
        slop = (size_t) (MAX_ALLOC_CHUNK-min_request);
      /* Try to get space, if fail reduce slop and try again */
      for (;;) {
        hdr_ptr = (small_pool_ptr) jpeg_get_small(cinfo, min_request + slop);
        if (hdr_ptr != NULL)
  	break;
        slop /= 2;
        if (slop < MIN_SLOP)	/* give up when it gets real small */
  	out_of_memory(cinfo, 2); /* jpeg_get_small failed */
      }
      mem->total_space_allocated += min_request + slop;
      /* Success, initialize the new pool header and add to end of list */
      hdr_ptr->hdr.next = NULL;
      hdr_ptr->hdr.bytes_used = 0;
      hdr_ptr->hdr.bytes_left = sizeofobject + slop;
      if (prev_hdr_ptr == NULL)	/* first pool in class? */
        mem->small_list[pool_id] = hdr_ptr;
      else
        prev_hdr_ptr->hdr.next = hdr_ptr;
    }
  
    /* OK, allocate the object from the current pool */
    data_ptr = (char *) (hdr_ptr + 1); /* point to first data byte in pool */
    data_ptr += hdr_ptr->hdr.bytes_used; /* point to place for object */
    hdr_ptr->hdr.bytes_used += sizeofobject;
    hdr_ptr->hdr.bytes_left -= sizeofobject;
  
    return (void *) data_ptr;
  }
  
  
  /*
   * Allocation of "large" objects.
   *
   * The external semantics of these are the same as "small" objects,
   * except that FAR pointers are used on 80x86.  However the pool
   * management heuristics are quite different.  We assume that each
   * request is large enough that it may as well be passed directly to
   * jpeg_get_large; the pool management just links everything together
   * so that we can free it all on demand.
   * Note: the major use of "large" objects is in JSAMPARRAY and JBLOCKARRAY
   * structures.  The routines that create these structures (see below)
   * deliberately bunch rows together to ensure a large request size.
   */
  
  METHODDEF(void FAR *)
  alloc_large (j_common_ptr cinfo, int pool_id, size_t sizeofobject)
  /* Allocate a "large" object */
  {
    my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
    large_pool_ptr hdr_ptr;
    size_t odd_bytes;
  
    /* Check for unsatisfiable request (do now to ensure no overflow below) */
    if (sizeofobject > (size_t) (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)))
      out_of_memory(cinfo, 3);	/* request exceeds malloc's ability */
  
    /* Round up the requested size to a multiple of SIZEOF(ALIGN_TYPE) */
    odd_bytes = sizeofobject % SIZEOF(ALIGN_TYPE);
    if (odd_bytes > 0)
      sizeofobject += SIZEOF(ALIGN_TYPE) - odd_bytes;
  
    /* Always make a new pool */
    if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)
      ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */
  
    hdr_ptr = (large_pool_ptr) jpeg_get_large(cinfo, sizeofobject +
  					    SIZEOF(large_pool_hdr));
    if (hdr_ptr == NULL)
      out_of_memory(cinfo, 4);	/* jpeg_get_large failed */
    mem->total_space_allocated += sizeofobject + SIZEOF(large_pool_hdr);
  
    /* Success, initialize the new pool header and add to list */
    hdr_ptr->hdr.next = mem->large_list[pool_id];
    /* We maintain space counts in each pool header for statistical purposes,
     * even though they are not needed for allocation.
     */
    hdr_ptr->hdr.bytes_used = sizeofobject;
    hdr_ptr->hdr.bytes_left = 0;
    mem->large_list[pool_id] = hdr_ptr;
  
    return (void FAR *) (hdr_ptr + 1); /* point to first data byte in pool */
  }
  
  
  /*
   * Creation of 2-D sample arrays.
   * The pointers are in near heap, the samples themselves in FAR heap.
   *
   * To minimize allocation overhead and to allow I/O of large contiguous
   * blocks, we allocate the sample rows in groups of as many rows as possible
   * without exceeding MAX_ALLOC_CHUNK total bytes per allocation request.
   * NB: the virtual array control routines, later in this file, know about
   * this chunking of rows.  The rowsperchunk value is left in the mem manager
   * object so that it can be saved away if this sarray is the workspace for
   * a virtual array.
   */
  
  METHODDEF(JSAMPARRAY)
  alloc_sarray (j_common_ptr cinfo, int pool_id,
  	      JDIMENSION samplesperrow, JDIMENSION numrows)
  /* Allocate a 2-D sample array */
  {
    my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
    JSAMPARRAY result;
    JSAMPROW workspace;
    JDIMENSION rowsperchunk, currow, i;
    long ltemp;
  
    /* Calculate max # of rows allowed in one allocation chunk */
    ltemp = (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)) /
  	  ((long) samplesperrow * SIZEOF(JSAMPLE));
    if (ltemp <= 0)
      ERREXIT(cinfo, JERR_WIDTH_OVERFLOW);
    if (ltemp < (long) numrows)
      rowsperchunk = (JDIMENSION) ltemp;
    else
      rowsperchunk = numrows;
    mem->last_rowsperchunk = rowsperchunk;
  
    /* Get space for row pointers (small object) */
    result = (JSAMPARRAY) alloc_small(cinfo, pool_id,
  				    (size_t) (numrows * SIZEOF(JSAMPROW)));
  
    /* Get the rows themselves (large objects) */
    currow = 0;
    while (currow < numrows) {
      rowsperchunk = MIN(rowsperchunk, numrows - currow);
      workspace = (JSAMPROW) alloc_large(cinfo, pool_id,
  	(size_t) ((size_t) rowsperchunk * (size_t) samplesperrow
  		  * SIZEOF(JSAMPLE)));
      for (i = rowsperchunk; i > 0; i--) {
        result[currow++] = workspace;
        workspace += samplesperrow;
      }
    }
  
    return result;
  }
  
  
  /*
   * Creation of 2-D coefficient-block arrays.
   * This is essentially the same as the code for sample arrays, above.
   */
  
  METHODDEF(JBLOCKARRAY)
  alloc_barray (j_common_ptr cinfo, int pool_id,
  	      JDIMENSION blocksperrow, JDIMENSION numrows)
  /* Allocate a 2-D coefficient-block array */
  {
    my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
    JBLOCKARRAY result;
    JBLOCKROW workspace;
    JDIMENSION rowsperchunk, currow, i;
    long ltemp;
  
    /* Calculate max # of rows allowed in one allocation chunk */
    ltemp = (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)) /
  	  ((long) blocksperrow * SIZEOF(JBLOCK));
    if (ltemp <= 0)
      ERREXIT(cinfo, JERR_WIDTH_OVERFLOW);
    if (ltemp < (long) numrows)
      rowsperchunk = (JDIMENSION) ltemp;
    else
      rowsperchunk = numrows;
    mem->last_rowsperchunk = rowsperchunk;
  
    /* Get space for row pointers (small object) */
    result = (JBLOCKARRAY) alloc_small(cinfo, pool_id,
  				     (size_t) (numrows * SIZEOF(JBLOCKROW)));
  
    /* Get the rows themselves (large objects) */
    currow = 0;
    while (currow < numrows) {
      rowsperchunk = MIN(rowsperchunk, numrows - currow);
      workspace = (JBLOCKROW) alloc_large(cinfo, pool_id,
  	(size_t) ((size_t) rowsperchunk * (size_t) blocksperrow
  		  * SIZEOF(JBLOCK)));
      for (i = rowsperchunk; i > 0; i--) {
        result[currow++] = workspace;
        workspace += blocksperrow;
      }
    }
  
    return result;
  }
  
  
  /*
   * About virtual array management:
   *
   * The above "normal" array routines are only used to allocate strip buffers
   * (as wide as the image, but just a few rows high).  Full-image-sized buffers
   * are handled as "virtual" arrays.  The array is still accessed a strip at a
   * time, but the memory manager must save the whole array for repeated
   * accesses.  The intended implementation is that there is a strip buffer in
   * memory (as high as is possible given the desired memory limit), plus a
   * backing file that holds the rest of the array.
   *
   * The request_virt_array routines are told the total size of the image and
   * the maximum number of rows that will be accessed at once.  The in-memory
   * buffer must be at least as large as the maxaccess value.
   *
   * The request routines create control blocks but not the in-memory buffers.
   * That is postponed until realize_virt_arrays is called.  At that time the
   * total amount of space needed is known (approximately, anyway), so free
   * memory can be divided up fairly.
   *
   * The access_virt_array routines are responsible for making a specific strip
   * area accessible (after reading or writing the backing file, if necessary).
   * Note that the access routines are told whether the caller intends to modify
   * the accessed strip; during a read-only pass this saves having to rewrite
   * data to disk.  The access routines are also responsible for pre-zeroing
   * any newly accessed rows, if pre-zeroing was requested.
   *
   * In current usage, the access requests are usually for nonoverlapping
   * strips; that is, successive access start_row numbers differ by exactly
   * num_rows = maxaccess.  This means we can get good performance with simple
   * buffer dump/reload logic, by making the in-memory buffer be a multiple
   * of the access height; then there will never be accesses across bufferload
   * boundaries.  The code will still work with overlapping access requests,
   * but it doesn't handle bufferload overlaps very efficiently.
   */
  
  
  METHODDEF(jvirt_sarray_ptr)
  request_virt_sarray (j_common_ptr cinfo, int pool_id, jboolean pre_zero,
  		     JDIMENSION samplesperrow, JDIMENSION numrows,
  		     JDIMENSION maxaccess)
  /* Request a virtual 2-D sample array */
  {
    my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
    jvirt_sarray_ptr result;
  
    /* Only IMAGE-lifetime virtual arrays are currently supported */
    if (pool_id != JPOOL_IMAGE)
      ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */
  
    /* get control block */
    result = (jvirt_sarray_ptr) alloc_small(cinfo, pool_id,
  					  SIZEOF(struct jvirt_sarray_control));
  
    result->mem_buffer = NULL;	/* marks array not yet realized */
    result->rows_in_array = numrows;
    result->samplesperrow = samplesperrow;
    result->maxaccess = maxaccess;
    result->pre_zero = pre_zero;
    result->b_s_open = FALSE;	/* no associated backing-store object */
    result->next = mem->virt_sarray_list; /* add to list of virtual arrays */
    mem->virt_sarray_list = result;
  
    return result;
  }
  
  
  METHODDEF(jvirt_barray_ptr)
  request_virt_barray (j_common_ptr cinfo, int pool_id, jboolean pre_zero,
  		     JDIMENSION blocksperrow, JDIMENSION numrows,
  		     JDIMENSION maxaccess)
  /* Request a virtual 2-D coefficient-block array */
  {
    my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
    jvirt_barray_ptr result;
  
    /* Only IMAGE-lifetime virtual arrays are currently supported */
    if (pool_id != JPOOL_IMAGE)
      ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */
  
    /* get control block */
    result = (jvirt_barray_ptr) alloc_small(cinfo, pool_id,
  					  SIZEOF(struct jvirt_barray_control));
  
    result->mem_buffer = NULL;	/* marks array not yet realized */
    result->rows_in_array = numrows;
    result->blocksperrow = blocksperrow;
    result->maxaccess = maxaccess;
    result->pre_zero = pre_zero;
    result->b_s_open = FALSE;	/* no associated backing-store object */
    result->next = mem->virt_barray_list; /* add to list of virtual arrays */
    mem->virt_barray_list = result;
  
    return result;
  }
  
  
  METHODDEF(void)
  realize_virt_arrays (j_common_ptr cinfo)
  /* Allocate the in-memory buffers for any unrealized virtual arrays */
  {
    my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
    long space_per_minheight, maximum_space, avail_mem;
    long minheights, max_minheights;
    jvirt_sarray_ptr sptr;
    jvirt_barray_ptr bptr;
  
    /* Compute the minimum space needed (maxaccess rows in each buffer)
     * and the maximum space needed (full image height in each buffer).
     * These may be of use to the system-dependent jpeg_mem_available routine.
     */
    space_per_minheight = 0;
    maximum_space = 0;
    for (sptr = mem->virt_sarray_list; sptr != NULL; sptr = sptr->next) {
      if (sptr->mem_buffer == NULL) { /* if not realized yet */
        space_per_minheight += (long) sptr->maxaccess *
  			     (long) sptr->samplesperrow * SIZEOF(JSAMPLE);
        maximum_space += (long) sptr->rows_in_array *
  		       (long) sptr->samplesperrow * SIZEOF(JSAMPLE);
      }
    }
    for (bptr = mem->virt_barray_list; bptr != NULL; bptr = bptr->next) {
      if (bptr->mem_buffer == NULL) { /* if not realized yet */
        space_per_minheight += (long) bptr->maxaccess *
  			     (long) bptr->blocksperrow * SIZEOF(JBLOCK);
        maximum_space += (long) bptr->rows_in_array *
  		       (long) bptr->blocksperrow * SIZEOF(JBLOCK);
      }
    }
  
    if (space_per_minheight <= 0)
      return;			/* no unrealized arrays, no work */
  
    /* Determine amount of memory to actually use; this is system-dependent. */
    avail_mem = jpeg_mem_available(cinfo, space_per_minheight, maximum_space,
  				 mem->total_space_allocated);
  
    /* If the maximum space needed is available, make all the buffers full
     * height; otherwise parcel it out with the same number of minheights
     * in each buffer.
     */
    if (avail_mem >= maximum_space)
      max_minheights = 1000000000L;
    else {
      max_minheights = avail_mem / space_per_minheight;
      /* If there doesn't seem to be enough space, try to get the minimum
       * anyway.  This allows a "stub" implementation of jpeg_mem_available().
       */
      if (max_minheights <= 0)
        max_minheights = 1;
    }
  
    /* Allocate the in-memory buffers and initialize backing store as needed. */
  
    for (sptr = mem->virt_sarray_list; sptr != NULL; sptr = sptr->next) {
      if (sptr->mem_buffer == NULL) { /* if not realized yet */
        minheights = ((long) sptr->rows_in_array - 1L) / sptr->maxaccess + 1L;
        if (minheights <= max_minheights) {
  	/* This buffer fits in memory */
  	sptr->rows_in_mem = sptr->rows_in_array;
        } else {
  	/* It doesn't fit in memory, create backing store. */
  	sptr->rows_in_mem = (JDIMENSION) (max_minheights * sptr->maxaccess);
  	jpeg_open_backing_store(cinfo, & sptr->b_s_info,
  				(long) sptr->rows_in_array *
  				(long) sptr->samplesperrow *
  				(long) SIZEOF(JSAMPLE));
  	sptr->b_s_open = TRUE;
        }
        sptr->mem_buffer = alloc_sarray(cinfo, JPOOL_IMAGE,
  				      sptr->samplesperrow, sptr->rows_in_mem);
        sptr->rowsperchunk = mem->last_rowsperchunk;
        sptr->cur_start_row = 0;
        sptr->first_undef_row = 0;
        sptr->dirty = FALSE;
      }
    }
  
    for (bptr = mem->virt_barray_list; bptr != NULL; bptr = bptr->next) {
      if (bptr->mem_buffer == NULL) { /* if not realized yet */
        minheights = ((long) bptr->rows_in_array - 1L) / bptr->maxaccess + 1L;
        if (minheights <= max_minheights) {
  	/* This buffer fits in memory */
  	bptr->rows_in_mem = bptr->rows_in_array;
        } else {
  	/* It doesn't fit in memory, create backing store. */
  	bptr->rows_in_mem = (JDIMENSION) (max_minheights * bptr->maxaccess);
  	jpeg_open_backing_store(cinfo, & bptr->b_s_info,
  				(long) bptr->rows_in_array *
  				(long) bptr->blocksperrow *
  				(long) SIZEOF(JBLOCK));
  	bptr->b_s_open = TRUE;
        }
        bptr->mem_buffer = alloc_barray(cinfo, JPOOL_IMAGE,
  				      bptr->blocksperrow, bptr->rows_in_mem);
        bptr->rowsperchunk = mem->last_rowsperchunk;
        bptr->cur_start_row = 0;
        bptr->first_undef_row = 0;
        bptr->dirty = FALSE;
      }
    }
  }
  
  
  LOCAL(void)
  do_sarray_io (j_common_ptr cinfo, jvirt_sarray_ptr ptr, jboolean writing)
  /* Do backing store read or write of a virtual sample array */
  {
    long bytesperrow, file_offset, byte_count, rows, thisrow, i;
  
    bytesperrow = (long) ptr->samplesperrow * SIZEOF(JSAMPLE);
    file_offset = ptr->cur_start_row * bytesperrow;
    /* Loop to read or write each allocation chunk in mem_buffer */
    for (i = 0; i < (long) ptr->rows_in_mem; i += ptr->rowsperchunk) {
      /* One chunk, but check for short chunk at end of buffer */
      rows = MIN((long) ptr->rowsperchunk, (long) ptr->rows_in_mem - i);
      /* Transfer no more than is currently defined */
      thisrow = (long) ptr->cur_start_row + i;
      rows = MIN(rows, (long) ptr->first_undef_row - thisrow);
      /* Transfer no more than fits in file */
      rows = MIN(rows, (long) ptr->rows_in_array - thisrow);
      if (rows <= 0)		/* this chunk might be past end of file! */
        break;
      byte_count = rows * bytesperrow;
      if (writing)
        (*ptr->b_s_info.write_backing_store) (cinfo, & ptr->b_s_info,
  					    (void FAR *) ptr->mem_buffer[i],
  					    file_offset, byte_count);
      else
        (*ptr->b_s_info.read_backing_store) (cinfo, & ptr->b_s_info,
  					   (void FAR *) ptr->mem_buffer[i],
  					   file_offset, byte_count);
      file_offset += byte_count;
    }
  }
  
  
  LOCAL(void)
  do_barray_io (j_common_ptr cinfo, jvirt_barray_ptr ptr, jboolean writing)
  /* Do backing store read or write of a virtual coefficient-block array */
  {
    long bytesperrow, file_offset, byte_count, rows, thisrow, i;
  
    bytesperrow = (long) ptr->blocksperrow * SIZEOF(JBLOCK);
    file_offset = ptr->cur_start_row * bytesperrow;
    /* Loop to read or write each allocation chunk in mem_buffer */
    for (i = 0; i < (long) ptr->rows_in_mem; i += ptr->rowsperchunk) {
      /* One chunk, but check for short chunk at end of buffer */
      rows = MIN((long) ptr->rowsperchunk, (long) ptr->rows_in_mem - i);
      /* Transfer no more than is currently defined */
      thisrow = (long) ptr->cur_start_row + i;
      rows = MIN(rows, (long) ptr->first_undef_row - thisrow);
      /* Transfer no more than fits in file */
      rows = MIN(rows, (long) ptr->rows_in_array - thisrow);
      if (rows <= 0)		/* this chunk might be past end of file! */
        break;
      byte_count = rows * bytesperrow;
      if (writing)
        (*ptr->b_s_info.write_backing_store) (cinfo, & ptr->b_s_info,
  					    (void FAR *) ptr->mem_buffer[i],
  					    file_offset, byte_count);
      else
        (*ptr->b_s_info.read_backing_store) (cinfo, & ptr->b_s_info,
  					   (void FAR *) ptr->mem_buffer[i],
  					   file_offset, byte_count);
      file_offset += byte_count;
    }
  }
  
  
  METHODDEF(JSAMPARRAY)
  access_virt_sarray (j_common_ptr cinfo, jvirt_sarray_ptr ptr,
  		    JDIMENSION start_row, JDIMENSION num_rows,
  		    jboolean writable)
  /* Access the part of a virtual sample array starting at start_row */
  /* and extending for num_rows rows.  writable is true if  */
  /* caller intends to modify the accessed area. */
  {
    JDIMENSION end_row = start_row + num_rows;
    JDIMENSION undef_row;
  
    /* debugging check */
    if (end_row > ptr->rows_in_array || num_rows > ptr->maxaccess ||
        ptr->mem_buffer == NULL)
      ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
  
    /* Make the desired part of the virtual array accessible */
    if (start_row < ptr->cur_start_row ||
        end_row > ptr->cur_start_row+ptr->rows_in_mem) {
      if (! ptr->b_s_open)
        ERREXIT(cinfo, JERR_VIRTUAL_BUG);
      /* Flush old buffer contents if necessary */
      if (ptr->dirty) {
        do_sarray_io(cinfo, ptr, TRUE);
        ptr->dirty = FALSE;
      }
      /* Decide what part of virtual array to access.
       * Algorithm: if target address > current window, assume forward scan,
       * load starting at target address.  If target address < current window,
       * assume backward scan, load so that target area is top of window.
       * Note that when switching from forward write to forward read, will have
       * start_row = 0, so the limiting case applies and we load from 0 anyway.
       */
      if (start_row > ptr->cur_start_row) {
        ptr->cur_start_row = start_row;
      } else {
        /* use long arithmetic here to avoid overflow & unsigned problems */
        long ltemp;
  
        ltemp = (long) end_row - (long) ptr->rows_in_mem;
        if (ltemp < 0)
  	ltemp = 0;		/* don't fall off front end of file */
        ptr->cur_start_row = (JDIMENSION) ltemp;
      }
      /* Read in the selected part of the array.
       * During the initial write pass, we will do no actual read
       * because the selected part is all undefined.
       */
      do_sarray_io(cinfo, ptr, FALSE);
    }
    /* Ensure the accessed part of the array is defined; prezero if needed.
     * To improve locality of access, we only prezero the part of the array
     * that the caller is about to access, not the entire in-memory array.
     */
    if (ptr->first_undef_row < end_row) {
      if (ptr->first_undef_row < start_row) {
        if (writable)		/* writer skipped over a section of array */
  	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
        undef_row = start_row;	/* but reader is allowed to read ahead */
      } else {
        undef_row = ptr->first_undef_row;
      }
      if (writable)
        ptr->first_undef_row = end_row;
      if (ptr->pre_zero) {
        size_t bytesperrow = (size_t) ptr->samplesperrow * SIZEOF(JSAMPLE);
        undef_row -= ptr->cur_start_row; /* make indexes relative to buffer */
        end_row -= ptr->cur_start_row;
        while (undef_row < end_row) {
  	jzero_far((void FAR *) ptr->mem_buffer[undef_row], bytesperrow);
  	undef_row++;
        }
      } else {
        if (! writable)		/* reader looking at undefined data */
  	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
      }
    }
    /* Flag the buffer dirty if caller will write in it */
    if (writable)
      ptr->dirty = TRUE;
    /* Return address of proper part of the buffer */
    return ptr->mem_buffer + (start_row - ptr->cur_start_row);
  }
  
  
  METHODDEF(JBLOCKARRAY)
  access_virt_barray (j_common_ptr cinfo, jvirt_barray_ptr ptr,
  		    JDIMENSION start_row, JDIMENSION num_rows,
  		    jboolean writable)
  /* Access the part of a virtual block array starting at start_row */
  /* and extending for num_rows rows.  writable is true if  */
  /* caller intends to modify the accessed area. */
  {
    JDIMENSION end_row = start_row + num_rows;
    JDIMENSION undef_row;
  
    /* debugging check */
    if (end_row > ptr->rows_in_array || num_rows > ptr->maxaccess ||
        ptr->mem_buffer == NULL)
      ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
  
    /* Make the desired part of the virtual array accessible */
    if (start_row < ptr->cur_start_row ||
        end_row > ptr->cur_start_row+ptr->rows_in_mem) {
      if (! ptr->b_s_open)
        ERREXIT(cinfo, JERR_VIRTUAL_BUG);
      /* Flush old buffer contents if necessary */
      if (ptr->dirty) {
        do_barray_io(cinfo, ptr, TRUE);
        ptr->dirty = FALSE;
      }
      /* Decide what part of virtual array to access.
       * Algorithm: if target address > current window, assume forward scan,
       * load starting at target address.  If target address < current window,
       * assume backward scan, load so that target area is top of window.
       * Note that when switching from forward write to forward read, will have
       * start_row = 0, so the limiting case applies and we load from 0 anyway.
       */
      if (start_row > ptr->cur_start_row) {
        ptr->cur_start_row = start_row;
      } else {
        /* use long arithmetic here to avoid overflow & unsigned problems */
        long ltemp;
  
        ltemp = (long) end_row - (long) ptr->rows_in_mem;
        if (ltemp < 0)
  	ltemp = 0;		/* don't fall off front end of file */
        ptr->cur_start_row = (JDIMENSION) ltemp;
      }
      /* Read in the selected part of the array.
       * During the initial write pass, we will do no actual read
       * because the selected part is all undefined.
       */
      do_barray_io(cinfo, ptr, FALSE);
    }
    /* Ensure the accessed part of the array is defined; prezero if needed.
     * To improve locality of access, we only prezero the part of the array
     * that the caller is about to access, not the entire in-memory array.
     */
    if (ptr->first_undef_row < end_row) {
      if (ptr->first_undef_row < start_row) {
        if (writable)		/* writer skipped over a section of array */
  	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
        undef_row = start_row;	/* but reader is allowed to read ahead */
      } else {
        undef_row = ptr->first_undef_row;
      }
      if (writable)
        ptr->first_undef_row = end_row;
      if (ptr->pre_zero) {
        size_t bytesperrow = (size_t) ptr->blocksperrow * SIZEOF(JBLOCK);
        undef_row -= ptr->cur_start_row; /* make indexes relative to buffer */
        end_row -= ptr->cur_start_row;
        while (undef_row < end_row) {
  	jzero_far((void FAR *) ptr->mem_buffer[undef_row], bytesperrow);
  	undef_row++;
        }
      } else {
        if (! writable)		/* reader looking at undefined data */
  	ERREXIT(cinfo, JERR_BAD_VIRTUAL_ACCESS);
      }
    }
    /* Flag the buffer dirty if caller will write in it */
    if (writable)
      ptr->dirty = TRUE;
    /* Return address of proper part of the buffer */
    return ptr->mem_buffer + (start_row - ptr->cur_start_row);
  }
  
  
  /*
   * Release all objects belonging to a specified pool.
   */
  
  METHODDEF(void)
  free_pool (j_common_ptr cinfo, int pool_id)
  {
    my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
    small_pool_ptr shdr_ptr;
    large_pool_ptr lhdr_ptr;
    size_t space_freed;
  
    if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)
      ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */
  
  #ifdef MEM_STATS
    if (cinfo->err->trace_level > 1)
      print_mem_stats(cinfo, pool_id); /* print pool's memory usage statistics */
  #endif
  
    /* If freeing IMAGE pool, close any virtual arrays first */
    if (pool_id == JPOOL_IMAGE) {
      jvirt_sarray_ptr sptr;
      jvirt_barray_ptr bptr;
  
      for (sptr = mem->virt_sarray_list; sptr != NULL; sptr = sptr->next) {
        if (sptr->b_s_open) {	/* there may be no backing store */
  	sptr->b_s_open = FALSE;	/* prevent recursive close if error */
  	(*sptr->b_s_info.close_backing_store) (cinfo, & sptr->b_s_info);
        }
      }
      mem->virt_sarray_list = NULL;
      for (bptr = mem->virt_barray_list; bptr != NULL; bptr = bptr->next) {
        if (bptr->b_s_open) {	/* there may be no backing store */
  	bptr->b_s_open = FALSE;	/* prevent recursive close if error */
  	(*bptr->b_s_info.close_backing_store) (cinfo, & bptr->b_s_info);
        }
      }
      mem->virt_barray_list = NULL;
    }
  
    /* Release large objects */
    lhdr_ptr = mem->large_list[pool_id];
    mem->large_list[pool_id] = NULL;
  
    while (lhdr_ptr != NULL) {
      large_pool_ptr next_lhdr_ptr = lhdr_ptr->hdr.next;
      space_freed = lhdr_ptr->hdr.bytes_used +
  		  lhdr_ptr->hdr.bytes_left +
  		  SIZEOF(large_pool_hdr);
      jpeg_free_large(cinfo, (void FAR *) lhdr_ptr, space_freed);
      mem->total_space_allocated -= space_freed;
      lhdr_ptr = next_lhdr_ptr;
    }
  
    /* Release small objects */
    shdr_ptr = mem->small_list[pool_id];
    mem->small_list[pool_id] = NULL;
  
    while (shdr_ptr != NULL) {
      small_pool_ptr next_shdr_ptr = shdr_ptr->hdr.next;
      space_freed = shdr_ptr->hdr.bytes_used +
  		  shdr_ptr->hdr.bytes_left +
  		  SIZEOF(small_pool_hdr);
      jpeg_free_small(cinfo, (void *) shdr_ptr, space_freed);
      mem->total_space_allocated -= space_freed;
      shdr_ptr = next_shdr_ptr;
    }
  }
  
  
  /*
   * Close up shop entirely.
   * Note that this cannot be called unless cinfo->mem is non-NULL.
   */
  
  METHODDEF(void)
  self_destruct (j_common_ptr cinfo)
  {
    int pool;
  
    /* Close all backing store, release all memory.
     * Releasing pools in reverse order might help avoid fragmentation
     * with some (brain-damaged) malloc libraries.
     */
    for (pool = JPOOL_NUMPOOLS-1; pool >= JPOOL_PERMANENT; pool--) {
      free_pool(cinfo, pool);
    }
  
    /* Release the memory manager control block too. */
    jpeg_free_small(cinfo, (void *) cinfo->mem, SIZEOF(my_memory_mgr));
    cinfo->mem = NULL;		/* ensures I will be called only once */
  
    jpeg_mem_term(cinfo);		/* system-dependent cleanup */
  }
  
  
  /*
   * Memory manager initialization.
   * When this is called, only the error manager pointer is valid in cinfo!
   */
  
  GLOBAL(void)
  jinit_memory_mgr (j_common_ptr cinfo)
  {
    my_mem_ptr mem;
    long max_to_use;
    int pool;
    size_t test_mac;
  
    cinfo->mem = NULL;		/* for safety if init fails */
  
    /* Check for configuration errors.
     * SIZEOF(ALIGN_TYPE) should be a power of 2; otherwise, it probably
     * doesn't reflect any real hardware alignment requirement.
     * The test is a little tricky: for X>0, X and X-1 have no one-bits
     * in common if and only if X is a power of 2, ie has only one one-bit.
     * Some compilers may give an "unreachable code" warning here; ignore it.
     */
    if ((SIZEOF(ALIGN_TYPE) & (SIZEOF(ALIGN_TYPE)-1)) != 0)
      ERREXIT(cinfo, JERR_BAD_ALIGN_TYPE);
    /* MAX_ALLOC_CHUNK must be representable as type size_t, and must be
     * a multiple of SIZEOF(ALIGN_TYPE).
     * Again, an "unreachable code" warning may be ignored here.
     * But a "constant too large" warning means you need to fix MAX_ALLOC_CHUNK.
     */
    test_mac = (size_t) MAX_ALLOC_CHUNK;
    if ((long) test_mac != MAX_ALLOC_CHUNK ||
        (MAX_ALLOC_CHUNK % SIZEOF(ALIGN_TYPE)) != 0)
      ERREXIT(cinfo, JERR_BAD_ALLOC_CHUNK);
  
    max_to_use = jpeg_mem_init(cinfo); /* system-dependent initialization */
  
    /* Attempt to allocate memory manager's control block */
    mem = (my_mem_ptr) jpeg_get_small(cinfo, SIZEOF(my_memory_mgr));
  
    if (mem == NULL) {
      jpeg_mem_term(cinfo);	/* system-dependent cleanup */
      ERREXIT1(cinfo, JERR_OUT_OF_MEMORY, 0);
    }
  
    /* OK, fill in the method pointers */
    mem->pub.alloc_small = alloc_small;
    mem->pub.alloc_large = alloc_large;
    mem->pub.alloc_sarray = alloc_sarray;
    mem->pub.alloc_barray = alloc_barray;
    mem->pub.request_virt_sarray = request_virt_sarray;
    mem->pub.request_virt_barray = request_virt_barray;
    mem->pub.realize_virt_arrays = realize_virt_arrays;
    mem->pub.access_virt_sarray = access_virt_sarray;
    mem->pub.access_virt_barray = access_virt_barray;
    mem->pub.free_pool = free_pool;
    mem->pub.self_destruct = self_destruct;
  
    /* Make MAX_ALLOC_CHUNK accessible to other modules */
    mem->pub.max_alloc_chunk = MAX_ALLOC_CHUNK;
  
    /* Initialize working state */
    mem->pub.max_memory_to_use = max_to_use;
  
    for (pool = JPOOL_NUMPOOLS-1; pool >= JPOOL_PERMANENT; pool--) {
      mem->small_list[pool] = NULL;
      mem->large_list[pool] = NULL;
    }
    mem->virt_sarray_list = NULL;
    mem->virt_barray_list = NULL;
  
    mem->total_space_allocated = SIZEOF(my_memory_mgr);
  
    /* Declare ourselves open for business */
    cinfo->mem = & mem->pub;
  
    /* Check for an environment variable JPEGMEM; if found, override the
     * default max_memory setting from jpeg_mem_init.  Note that the
     * surrounding application may again override this value.
     * If your system doesn't support getenv(), define NO_GETENV to disable
     * this feature.
     */
  #ifndef NO_GETENV
    { char * memenv;
  
      if ((memenv = getenv("JPEGMEM")) != NULL) {
        char ch = 'x';
  
        if (sscanf(memenv, "%ld%c", &max_to_use, &ch) > 0) {
  	if (ch == 'm' || ch == 'M')
  	  max_to_use *= 1000L;
  	mem->pub.max_memory_to_use = max_to_use * 1000L;
        }
      }
    }
  #endif
  
  }
  