482 lines
14 KiB
C
482 lines
14 KiB
C
/*
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* jwrgif.c
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*
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* Copyright (C) 1991, 1992, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This file contains routines to write output images in GIF format.
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*
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* These routines may need modification for non-Unix environments or
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* specialized applications. As they stand, they assume output to
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* an ordinary stdio stream.
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*
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* These routines are invoked via the methods put_pixel_rows, put_color_map,
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* and output_init/term.
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*/
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/*
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* This code is loosely based on ppmtogif from the PBMPLUS distribution
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* of Feb. 1991. That file contains the following copyright notice:
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* Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>.
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* Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al.
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* Copyright (C) 1989 by Jef Poskanzer.
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* Permission to use, copy, modify, and distribute this software and its
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* documentation for any purpose and without fee is hereby granted, provided
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* that the above copyright notice appear in all copies and that both that
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* copyright notice and this permission notice appear in supporting
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* documentation. This software is provided "as is" without express or
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* implied warranty.
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*
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* We are also required to state that
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* "The Graphics Interchange Format(c) is the Copyright property of
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* CompuServe Incorporated. GIF(sm) is a Service Mark property of
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* CompuServe Incorporated."
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*/
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#include "jinclude.h"
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#ifdef GIF_SUPPORTED
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static decompress_info_ptr dcinfo; /* to avoid passing to all functions */
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#define MAX_LZW_BITS 12 /* maximum LZW code size (4096 symbols) */
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typedef INT16 code_int; /* must hold -1 .. 2**MAX_LZW_BITS */
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#define LZW_TABLE_SIZE ((code_int) 1 << MAX_LZW_BITS)
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#define HSIZE 5003 /* hash table size for 80% occupancy */
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typedef int hash_int; /* must hold -2*HSIZE..2*HSIZE */
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static int n_bits; /* current number of bits/code */
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static code_int maxcode; /* maximum code, given n_bits */
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#define MAXCODE(n_bits) (((code_int) 1 << (n_bits)) - 1)
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static int init_bits; /* initial n_bits ... restored after clear */
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static code_int ClearCode; /* clear code (doesn't change) */
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static code_int EOFCode; /* EOF code (ditto) */
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static code_int free_code; /* first not-yet-used symbol code */
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/*
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* The LZW hash table consists of three parallel arrays:
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* hash_code[i] code of symbol in slot i, or 0 if empty slot
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* hash_prefix[i] symbol's prefix code; undefined if empty slot
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* hash_suffix[i] symbol's suffix character; undefined if empty slot
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* where slot values (i) range from 0 to HSIZE-1.
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*
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* Algorithm: use open addressing double hashing (no chaining) on the
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* prefix code / suffix character combination. We do a variant of Knuth's
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* algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
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* secondary probe.
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*
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* The hash tables are allocated from FAR heap space since they would use up
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* rather a lot of the near data space in a PC.
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*/
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static code_int FAR *hash_code; /* => hash table of symbol codes */
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static code_int FAR *hash_prefix; /* => hash table of prefix symbols */
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static UINT8 FAR *hash_suffix; /* => hash table of suffix bytes */
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/*
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* Routines to package compressed data bytes into GIF data blocks.
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* A data block consists of a count byte (1..255) and that many data bytes.
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*/
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static int bytesinpkt; /* # of bytes in current packet */
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static char packetbuf[256]; /* workspace for accumulating packet */
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LOCAL void
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flush_packet (void)
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/* flush any accumulated data */
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{
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if (bytesinpkt > 0) { /* never write zero-length packet */
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packetbuf[0] = (char) bytesinpkt++;
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if (JFWRITE(dcinfo->output_file, packetbuf, bytesinpkt)
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!= (size_t) bytesinpkt)
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ERREXIT(dcinfo->emethods, "Output file write error");
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bytesinpkt = 0;
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}
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}
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/* Add a character to current packet; flush to disk if necessary */
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#define CHAR_OUT(c) \
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{ packetbuf[++bytesinpkt] = (char) (c); \
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if (bytesinpkt >= 255) \
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flush_packet(); \
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}
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/* Routine to convert variable-width codes into a byte stream */
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static INT32 cur_accum; /* holds bits not yet output */
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static int cur_bits; /* # of bits in cur_accum */
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LOCAL void
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output (code_int code)
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/* Emit a code of n_bits bits */
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/* Uses cur_accum and cur_bits to reblock into 8-bit bytes */
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{
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cur_accum |= ((INT32) code) << cur_bits;
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cur_bits += n_bits;
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while (cur_bits >= 8) {
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CHAR_OUT(cur_accum & 0xFF);
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cur_accum >>= 8;
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cur_bits -= 8;
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}
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/*
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* If the next entry is going to be too big for the code size,
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* then increase it, if possible. We do this here to ensure
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* that it's done in sync with the decoder's codesize increases.
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*/
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if (free_code > maxcode) {
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n_bits++;
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if (n_bits == MAX_LZW_BITS)
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maxcode = LZW_TABLE_SIZE; /* free_code will never exceed this */
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else
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maxcode = MAXCODE(n_bits);
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}
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}
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/* The LZW algorithm proper */
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static code_int waiting_code; /* symbol not yet output; may be extendable */
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static boolean first_byte; /* if TRUE, waiting_code is not valid */
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LOCAL void
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clear_hash (void)
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/* Fill the hash table with empty entries */
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{
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/* It's sufficient to zero hash_code[] */
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jzero_far((void FAR *) hash_code, HSIZE * SIZEOF(code_int));
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}
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LOCAL void
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clear_block (void)
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/* Reset compressor and issue a Clear code */
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{
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clear_hash(); /* delete all the symbols */
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free_code = ClearCode + 2;
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output(ClearCode); /* inform decoder */
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n_bits = init_bits; /* reset code size */
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maxcode = MAXCODE(n_bits);
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}
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LOCAL void
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compress_init (int i_bits)
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/* Initialize LZW compressor */
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{
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/* init all the static variables */
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n_bits = init_bits = i_bits;
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maxcode = MAXCODE(n_bits);
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ClearCode = ((code_int) 1 << (init_bits - 1));
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EOFCode = ClearCode + 1;
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free_code = ClearCode + 2;
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first_byte = TRUE; /* no waiting symbol yet */
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/* init output buffering vars */
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bytesinpkt = 0;
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cur_accum = 0;
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cur_bits = 0;
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/* clear hash table */
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clear_hash();
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/* GIF specifies an initial Clear code */
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output(ClearCode);
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}
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LOCAL void
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compress_byte (int c)
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/* Accept and compress one 8-bit byte */
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{
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register hash_int i;
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register hash_int disp;
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if (first_byte) { /* need to initialize waiting_code */
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waiting_code = c;
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first_byte = FALSE;
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return;
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}
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/* Probe hash table to see if a symbol exists for
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* waiting_code followed by c.
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* If so, replace waiting_code by that symbol and return.
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*/
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i = ((hash_int) c << (MAX_LZW_BITS-8)) + waiting_code;
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/* i is less than twice 2**MAX_LZW_BITS, therefore less than twice HSIZE */
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if (i >= HSIZE)
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i -= HSIZE;
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if (hash_code[i] != 0) { /* is first probed slot empty? */
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if (hash_prefix[i] == waiting_code && hash_suffix[i] == (UINT8) c) {
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waiting_code = hash_code[i];
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return;
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}
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if (i == 0) /* secondary hash (after G. Knott) */
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disp = 1;
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else
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disp = HSIZE - i;
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while (1) {
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i -= disp;
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if (i < 0)
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i += HSIZE;
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if (hash_code[i] == 0)
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break; /* hit empty slot */
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if (hash_prefix[i] == waiting_code && hash_suffix[i] == (UINT8) c) {
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waiting_code = hash_code[i];
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return;
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}
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}
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}
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/* here when hashtable[i] is an empty slot; desired symbol not in table */
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output(waiting_code);
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if (free_code < LZW_TABLE_SIZE) {
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hash_code[i] = free_code++; /* add symbol to hashtable */
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hash_prefix[i] = waiting_code;
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hash_suffix[i] = (UINT8) c;
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} else
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clear_block();
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waiting_code = c;
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}
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LOCAL void
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compress_term (void)
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/* Clean up at end */
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{
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/* Flush out the buffered code */
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if (! first_byte)
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output(waiting_code);
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/* Send an EOF code */
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output(EOFCode);
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/* Flush the bit-packing buffer */
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if (cur_bits > 0) {
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CHAR_OUT(cur_accum & 0xFF);
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}
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/* Flush the packet buffer */
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flush_packet();
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}
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/* GIF header construction */
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LOCAL void
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put_word (UINT16 w)
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/* Emit a 16-bit word, LSB first */
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{
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putc(w & 0xFF, dcinfo->output_file);
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putc((w >> 8) & 0xFF, dcinfo->output_file);
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}
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LOCAL void
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put_3bytes (int val)
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/* Emit 3 copies of same byte value --- handy subr for colormap construction */
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{
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putc(val, dcinfo->output_file);
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putc(val, dcinfo->output_file);
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putc(val, dcinfo->output_file);
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}
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LOCAL void
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emit_header (int num_colors, JSAMPARRAY colormap)
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/* Output the GIF file header, including color map */
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/* If colormap==NULL, synthesize a gray-scale colormap */
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{
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int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte;
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int cshift = dcinfo->data_precision - 8;
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int i;
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if (num_colors > 256)
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ERREXIT(dcinfo->emethods, "GIF can only handle 256 colors");
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/* Compute bits/pixel and related values */
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BitsPerPixel = 1;
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while (num_colors > (1 << BitsPerPixel))
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BitsPerPixel++;
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ColorMapSize = 1 << BitsPerPixel;
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if (BitsPerPixel <= 1)
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InitCodeSize = 2;
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else
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InitCodeSize = BitsPerPixel;
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/*
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* Write the GIF header.
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* Note that we generate a plain GIF87 header for maximum compatibility.
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*/
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(void) JFWRITE(dcinfo->output_file, "GIF87a", 6);
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/* Write the Logical Screen Descriptor */
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put_word((UINT16) dcinfo->image_width);
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put_word((UINT16) dcinfo->image_height);
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FlagByte = 0x80; /* Yes, there is a global color table */
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FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */
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FlagByte |= (BitsPerPixel-1); /* size of global color table */
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putc(FlagByte, dcinfo->output_file);
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putc(0, dcinfo->output_file); /* Background color index */
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putc(0, dcinfo->output_file); /* Reserved in GIF87 (aspect ratio in GIF89) */
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/* Write the Global Color Map */
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/* If the color map is more than 8 bits precision, */
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/* we reduce it to 8 bits by shifting */
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for (i=0; i < ColorMapSize; i++) {
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if (i < num_colors) {
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if (colormap != NULL) {
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if (dcinfo->out_color_space == CS_RGB) {
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/* Normal case: RGB color map */
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putc(GETJSAMPLE(colormap[0][i]) >> cshift, dcinfo->output_file);
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putc(GETJSAMPLE(colormap[1][i]) >> cshift, dcinfo->output_file);
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putc(GETJSAMPLE(colormap[2][i]) >> cshift, dcinfo->output_file);
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} else {
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/* Grayscale "color map": possible if quantizing grayscale image */
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put_3bytes(GETJSAMPLE(colormap[0][i]) >> cshift);
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}
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} else {
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/* Create a gray-scale map of num_colors values, range 0..255 */
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put_3bytes((i * 255 + (num_colors-1)/2) / (num_colors-1));
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}
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} else {
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/* fill out the map to a power of 2 */
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put_3bytes(0);
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}
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}
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/* Write image separator and Image Descriptor */
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putc(',', dcinfo->output_file); /* separator */
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put_word((UINT16) 0); /* left/top offset */
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put_word((UINT16) 0);
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put_word((UINT16) dcinfo->image_width); /* image size */
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put_word((UINT16) dcinfo->image_height);
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/* flag byte: not interlaced, no local color map */
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putc(0x00, dcinfo->output_file);
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/* Write Initial Code Size byte */
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putc(InitCodeSize, dcinfo->output_file);
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/* Initialize for LZW compression of image data */
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compress_init(InitCodeSize+1);
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}
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/*
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* Initialize for GIF output.
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*/
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METHODDEF void
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output_init (decompress_info_ptr cinfo)
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{
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dcinfo = cinfo; /* save for use by local routines */
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if (cinfo->final_out_comps != 1) /* safety check */
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ERREXIT(cinfo->emethods, "GIF output got confused");
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/* Allocate space for hash table */
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hash_code = (code_int FAR *) (*cinfo->emethods->alloc_medium)
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(HSIZE * SIZEOF(code_int));
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hash_prefix = (code_int FAR *) (*cinfo->emethods->alloc_medium)
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(HSIZE * SIZEOF(code_int));
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hash_suffix = (UINT8 FAR *) (*cinfo->emethods->alloc_medium)
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(HSIZE * SIZEOF(UINT8));
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/*
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* If we aren't quantizing, put_color_map won't be called,
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* so emit the header now. This only happens with gray scale output.
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* (If we are quantizing, wait for the color map to be provided.)
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*/
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if (! cinfo->quantize_colors)
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emit_header(256, (JSAMPARRAY) NULL);
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}
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/*
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* Write the color map.
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*/
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METHODDEF void
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put_color_map (decompress_info_ptr cinfo, int num_colors, JSAMPARRAY colormap)
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{
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emit_header(num_colors, colormap);
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}
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/*
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* Write some pixel data.
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*/
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METHODDEF void
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put_pixel_rows (decompress_info_ptr cinfo, int num_rows,
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JSAMPIMAGE pixel_data)
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{
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register JSAMPROW ptr;
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register long col;
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register long width = cinfo->image_width;
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register int row;
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for (row = 0; row < num_rows; row++) {
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ptr = pixel_data[0][row];
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for (col = width; col > 0; col--) {
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compress_byte(GETJSAMPLE(*ptr));
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ptr++;
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}
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}
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}
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/*
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* Finish up at the end of the file.
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*/
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METHODDEF void
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output_term (decompress_info_ptr cinfo)
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{
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/* Flush LZW mechanism */
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compress_term();
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/* Write a zero-length data block to end the series */
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putc(0, cinfo->output_file);
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/* Write the GIF terminator mark */
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putc(';', cinfo->output_file);
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/* Make sure we wrote the output file OK */
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fflush(cinfo->output_file);
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if (ferror(cinfo->output_file))
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ERREXIT(cinfo->emethods, "Output file write error");
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/* Free space */
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/* no work (we let free_all release the workspace) */
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}
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/*
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* The method selection routine for GIF format output.
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* This should be called from d_ui_method_selection if GIF output is wanted.
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*/
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GLOBAL void
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jselwgif (decompress_info_ptr cinfo)
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{
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cinfo->methods->output_init = output_init;
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cinfo->methods->put_color_map = put_color_map;
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cinfo->methods->put_pixel_rows = put_pixel_rows;
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cinfo->methods->output_term = output_term;
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if (cinfo->out_color_space != CS_GRAYSCALE &&
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cinfo->out_color_space != CS_RGB)
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ERREXIT(cinfo->emethods, "GIF output must be grayscale or RGB");
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/* Force quantization if color or if > 8 bits input */
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if (cinfo->out_color_space == CS_RGB || cinfo->data_precision > 8) {
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/* Force quantization to at most 256 colors */
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cinfo->quantize_colors = TRUE;
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if (cinfo->desired_number_of_colors > 256)
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cinfo->desired_number_of_colors = 256;
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}
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}
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#endif /* GIF_SUPPORTED */
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