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src/Source/LibJPEG/wrgif.c  view on Meta::CPAN

/*
 * wrgif.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 routines to write output images in GIF format.
 *
 **************************************************************************
 * NOTE: to avoid entanglements with Unisys' patent on LZW compression,   *
 * this code has been modified to output "uncompressed GIF" files.        *
 * There is no trace of the LZW algorithm in this file.                   *
 **************************************************************************
 *
 * These routines may need modification for non-Unix environments or
 * specialized applications.  As they stand, they assume output to
 * an ordinary stdio stream.
 */

/*
 * This code is loosely based on ppmtogif from the PBMPLUS distribution
 * of Feb. 1991.  That file contains the following copyright notice:
 *    Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>.
 *    Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al.
 *    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.
 *
 * 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


/* Private version of data destination object */

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

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

  /* State for packing variable-width codes into a bitstream */
  int n_bits;			/* current number of bits/code */
  int maxcode;			/* maximum code, given n_bits */
  INT32 cur_accum;		/* holds bits not yet output */
  int cur_bits;			/* # of bits in cur_accum */

  /* State for GIF code assignment */
  int ClearCode;		/* clear code (doesn't change) */
  int EOFCode;			/* EOF code (ditto) */
  int code_counter;		/* counts output symbols */

  /* GIF data packet construction buffer */
  int bytesinpkt;		/* # of bytes in current packet */
  char packetbuf[256];		/* workspace for accumulating packet */

} gif_dest_struct;

typedef gif_dest_struct * gif_dest_ptr;

/* Largest value that will fit in N bits */
#define MAXCODE(n_bits)	((1 << (n_bits)) - 1)


/*
 * Routines to package finished data bytes into GIF data blocks.