text: /* mgrtopbm.c - read a MGR bitmap and produce a portable bitmap
  **
  ** Copyright (C) 1989 by Jef Poskanzer.
  **
  ** Permission to use, copy, modify, and distribute this software and its
  ** documentation for any purpose and without fee is hereby granted, provided
  ** that the above copyright notice appear in all copies and that both that
  ** copyright notice and this permission notice appear in supporting
  ** documentation.  This software is provided "as is" without express or
  ** implied warranty.
  */
  
  #include <string.h>
  #include <errno.h>
  
  #include "pbm.h"
  #include "mgr.h"
  
  
  static unsigned char item;
  static int bitsperitem, bitshift;
  
  static void
  getinit(FILE * const file, 
          int *  const colsP, 
          int *  const rowsP, 
          int *  const depthP, 
          int *  const padrightP,
          int *  const bitsperitemP) {
  
      struct b_header head;
      int pad;
  
      if (fread(&head, sizeof(struct old_b_header), 1, file ) != 1)
          pm_error("Unable to read 1st byte of file.  "
                   "fread() returns errno %d (%s)",
                   errno, strerror(errno));
      if (head.magic[0] == 'y' && head.magic[1] == 'z') { 
          /* new style bitmap */
          if (fread(&head.depth, 
                    sizeof(head) - sizeof(struct old_b_header), 1, file) 
               != 1 )
              pm_error("Unable to read header after 1st byte.  "
                       "fread() returns errno %d (%s)",
                       errno, strerror(errno));
          *depthP = (int) head.depth - ' ';
          pad = 8;
      } else if (head.magic[0] == 'x' && head.magic[1] == 'z') { 
          /* old style bitmap with 32-bit padding */
          *depthP = 1;
          pad = 32;
      } else if (head.magic[0] == 'z' && head.magic[1] == 'z') { 
          /* old style bitmap with 16-bit padding */
          *depthP = 1;
          pad = 16;
      } else if (head.magic[0] == 'z' && head.magic[1] == 'y') {
          /* old style 8-bit pixmap with 16-bit padding */
          *depthP = 8;
          pad = 16;
      } else {
          pm_error("bad magic chars in MGR file: '%c%c'",
                   head.magic[0], head.magic[1] );
          pad = -1;  /* should never reach here */
      }
  
      if (head.h_wide < ' ' || head.l_wide < ' ')
          pm_error("Invalid width field in MGR header");
      if (head.h_high < ' ' || head.l_high < ' ')
          pm_error("Invalid width field in MGR header");
      
      overflow_add(*colsP, pad);
  
      *colsP = (((int)head.h_wide - ' ') << 6) + ((int)head.l_wide - ' ');
      *rowsP = (((int)head.h_high - ' ') << 6) + ((int) head.l_high - ' ');
      *padrightP = ( ( *colsP + pad - 1 ) / pad ) * pad - *colsP;
      
      *bitsperitemP = 8;
  }
  
  
  
  static bit
  getbit( file )
      FILE* file;
      {
      bit b;
  
      if ( bitsperitem == 8 )
  	{
  	item = getc( file );
  	bitsperitem = 0;
  	bitshift = 7;
  	}
      bitsperitem++;
      b = ( ( item >> bitshift) & 1 ) ? PBM_BLACK : PBM_WHITE;
      bitshift--;
      return b;
      }
  
  
  
  int
  main( argc, argv )
      int argc;
      char* argv[];
      {
      FILE* ifp;
      bit* bitrow;
      register bit* bP;
      int rows, cols, depth, padright, row, col;
  
  
      pbm_init( &argc, argv );
  
      if ( argc > 2 )
  	pm_usage( "[mgrfile]" );
  
      if ( argc == 2 )
  	ifp = pm_openr( argv[1] );
      else
  	ifp = stdin;
  
      getinit( ifp, &cols, &rows, &depth, &padright, &bitsperitem );
      if ( depth != 1 )
  	pm_error( "MGR file has depth of %d, must be 1", depth );
  
      pbm_writepbminit( stdout, cols, rows, 0 );
      bitrow = pbm_allocrow( cols );
  
      for ( row = 0; row < rows; row++ )
  	{
  	/* Get data, bit-reversed within each byte. */
          for ( col = 0, bP = bitrow; col < cols; col++, bP++ )
  	    *bP = getbit( ifp );
  	/* Discard line padding */
          for ( col = 0; col < padright; col ++ )
  	    (void) getbit( ifp );
  	pbm_writepbmrow( stdout, bitrow, cols, 0 );
  	}
  
      pm_close( ifp );
      pm_close( stdout );
  
      exit( 0 );
      }
  
  
  