JPEGView/Independent JPEG Group/rdgif.c

/*
 * rdgif.c
 *
 * Copyright (C) 1991-1994, 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 routines to read input images in GIF format.
 *
 * These routines may need modification for non-Unix environments or
 * specialized applications.  As they stand, they assume input from
 * an ordinary stdio stream.  They further assume that reading begins
 * at the start of the file; input_init may need work if the
 * user interface has already read some data (e.g., to determine that
 * the file is indeed GIF format).
 */

/*
 * This code is loosely based on giftoppm from the PBMPLUS distribution
 * of Feb. 1991.  That file contains the following copyright notice:
 * +-------------------------------------------------------------------+
 * | Copyright 1990, David Koblas.                                     |
 * |   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.           |
 * +-------------------------------------------------------------------+
 *
 * We are also required to state that
 *    "The Graphics Interchange Format(c) is the Copyright property of
 *    CompuServe Incorporated. GIF(sm) is a Service Mark property of
 *    CompuServe Incorporated."
 */

#include "cdjpeg.h"		/* Common decls for cjpeg/djpeg applications */

#ifdef GIF_SUPPORTED


#define	MAXCOLORMAPSIZE	256	/* max # of colors in a GIF colormap */
#define NUMCOLORS	3	/* # of colors */
#define CM_RED		0	/* color component numbers */
#define CM_GREEN	1
#define CM_BLUE		2

#define	MAX_LZW_BITS	12	/* maximum LZW code size */
#define LZW_TABLE_SIZE	(1<<MAX_LZW_BITS) /* # of possible LZW symbols */

/* Macros for extracting header data --- note we assume chars may be signed */

#define LM_to_uint(a,b)		((((b)&0xFF) << 8) | ((a)&0xFF))

#define BitSet(byte, bit)	((byte) & (bit))
#define INTERLACE	0x40	/* mask for bit signifying interlaced image */
#define COLORMAPFLAG	0x80	/* mask for bit signifying colormap presence */

#define	ReadOK(file,buffer,len)	(JFREAD(file,buffer,len) == ((size_t) (len)))

/* LZW decompression tables look like this:
 *   symbol_head[K] = prefix symbol of any LZW symbol K (0..LZW_TABLE_SIZE-1)
 *   symbol_tail[K] = suffix byte   of any LZW symbol K (0..LZW_TABLE_SIZE-1)
 * Note that entries 0..end_code of the above tables are not used,
 * since those symbols represent raw bytes or special codes.
 *
 * The stack represents the not-yet-used expansion of the last LZW symbol.
 * In the worst case, a symbol could expand to as many bytes as there are
 * LZW symbols, so we allocate LZW_TABLE_SIZE bytes for the stack.
 * (This is conservative since that number includes the raw-byte symbols.)
 *
 * The tables are allocated from FAR heap space since they would use up
 * rather a lot of the near data space in a PC.
 */


/* Private version of data source object */

typedef struct {
  struct cjpeg_source_struct pub; /* public fields */

  j_compress_ptr cinfo;		/* back link saves passing separate parm */

  JSAMPARRAY colormap;		/* GIF colormap (converted to my format) */

  /* State for GetCode and LZWReadByte */
  char code_buf[256+4];		/* current input data block */
  int last_byte;		/* # of bytes in code_buf */
  int last_bit;			/* # of bits in code_buf */
  int cur_bit;			/* next bit index to read */
  boolean out_of_blocks;	/* TRUE if hit terminator data block */

  int input_code_size;		/* codesize given in GIF file */
  int clear_code,end_code;	/* values for Clear and End codes */

  int code_size;		/* current actual code size */
  int limit_code;		/* 2^code_size */
  int max_code;			/* first unused code value */
  boolean first_time;		/* flags first ca