libavcodec/lzw.c

   1 /*
   2  * LZW decoder
   3  * Copyright (c) 2003 Fabrice Bellard
   4  * Copyright (c) 2006 Konstantin Shishkov
   5  *
   6  * This file is part of FFmpeg.
   7  *
   8  * FFmpeg is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * FFmpeg is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with FFmpeg; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 /**
  24  * @file libavcodec/lzw.c
  25  * @brief LZW decoding routines
  26  * @author Fabrice Bellard
  27  * Modified for use in TIFF by Konstantin Shishkov
  28  */
  29
  30 #include "avcodec.h"
  31 #include "lzw.h"
  32
  33 #define LZW_MAXBITS                 12
  34 #define LZW_SIZTABLE                (1<<LZW_MAXBITS)
  35
  36 static const uint16_t mask[17] =
  37 {
  38     0x0000, 0x0001, 0x0003, 0x0007,
  39     0x000F, 0x001F, 0x003F, 0x007F,
  40     0x00FF, 0x01FF, 0x03FF, 0x07FF,
  41     0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
  42 };
  43
  44 struct LZWState {
  45     const uint8_t *pbuf, *ebuf;
  46     int bbits;
  47     unsigned int bbuf;
  48
  49     int mode;                   ///< Decoder mode
  50     int cursize;                ///< The current code size
  51     int curmask;
  52     int codesize;
  53     int clear_code;
  54     int end_code;
  55     int newcodes;               ///< First available code
  56     int top_slot;               ///< Highest code for current size
  57     int extra_slot;
  58     int slot;                   ///< Last read code
  59     int fc, oc;
  60     uint8_t *sp;
  61     uint8_t stack[LZW_SIZTABLE];
  62     uint8_t suffix[LZW_SIZTABLE];
  63     uint16_t prefix[LZW_SIZTABLE];
  64     int bs;                     ///< current buffer size for GIF
  65 };
  66
  67 /* get one code from stream */
  68 static int lzw_get_code(struct LZWState * s)
  69 {
  70     int c;
  71
  72     if(s->mode == FF_LZW_GIF) {
  73         while (s->bbits < s->cursize) {
  74             if (!s->bs) {
  75                 s->bs = *s->pbuf++;
  76             }
  77             s->bbuf |= (*s->pbuf++) << s->bbits;
  78             s->bbits += 8;
  79             s->bs--;
  80         }
  81         c = s->bbuf;
  82         s->bbuf >>= s->cursize;
  83     } else { // TIFF
  84         while (s->bbits < s->cursize) {
  85             s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
  86             s->bbits += 8;
  87         }
  88         c = s->bbuf >> (s->bbits - s->cursize);
  89     }
  90     s->bbits -= s->cursize;
  91     return c & s->curmask;
  92 }
  93
  94 const uint8_t* ff_lzw_cur_ptr(LZWState *p)
  95 {
  96     return ((struct LZWState*)p)->pbuf;
  97 }
  98
  99 void ff_lzw_decode_tail(LZWState *p)
 100 {
 101     struct LZWState *s = (struct LZWState *)p;
 102
 103     if(s->mode == FF_LZW_GIF) {
 104         while(s->pbuf < s->ebuf && s->bs>0){
 105             s->pbuf += s->bs;
 106             s->bs = *s->pbuf++;
 107         }
 108     }else
 109         s->pbuf= s->ebuf;
 110 }
 111
 112 av_cold void ff_lzw_decode_open(LZWState **p)
 113 {
 114     *p = av_mallocz(sizeof(struct LZWState));
 115 }
 116
 117 av_cold void ff_lzw_decode_close(LZWState **p)
 118 {
 119     av_freep(p);
 120 }
 121
 122 /**
 123  * Initialize LZW decoder
 124  * @param s LZW context
 125  * @param csize initial code size in bits
 126  * @param buf input data
 127  * @param buf_size input data size
 128  * @param mode decoder working mode - either GIF or TIFF
 129  */
 130 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
 131 {
 132     struct LZWState *s = (struct LZWState *)p;
 133
 134     if(csize < 1 || csize >= LZW_MAXBITS)
 135         return -1;
 136     /* read buffer */
 137     s->pbuf = buf;
 138     s->ebuf = s->pbuf + buf_size;
 139     s->bbuf = 0;
 140     s->bbits = 0;
 141     s->bs = 0;
 142
 143     /* decoder */
 144     s->codesize = csize;
 145     s->cursize = s->codesize + 1;
 146     s->curmask = mask[s->cursize];
 147     s->top_slot = 1 << s->cursize;
 148     s->clear_code = 1 << s->codesize;
 149     s->end_code = s->clear_code + 1;
 150     s->slot = s->newcodes = s->clear_code + 2;
 151     s->oc = s->fc = -1;
 152     s->sp = s->stack;
 153
 154     s->mode = mode;
 155     s->extra_slot = s->mode == FF_LZW_TIFF;
 156     return 0;
 157 }
 158
 159 /**
 160  * Decode given number of bytes
 161  * NOTE: the algorithm here is inspired from the LZW GIF decoder
 162  *  written by Steven A. Bennett in 1987.
 163  *
 164  * @param s LZW context
 165  * @param buf output buffer
 166  * @param len number of bytes to decode
 167  * @return number of bytes decoded
 168  */
 169 int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
 170     int l, c, code, oc, fc;
 171     uint8_t *sp;
 172     struct LZWState *s = (struct LZWState *)p;
 173
 174     if (s->end_code < 0)
 175         return 0;
 176
 177     l = len;
 178     sp = s->sp;
 179     oc = s->oc;
 180     fc = s->fc;
 181
 182     for (;;) {
 183         while (sp > s->stack) {
 184             *buf++ = *(--sp);
 185             if ((--l) == 0)
 186                 goto the_end;
 187         }
 188         c = lzw_get_code(s);
 189         if (c == s->end_code) {
 190             break;
 191         } else if (c == s->clear_code) {
 192             s->cursize = s->codesize + 1;
 193             s->curmask = mask[s->cursize];
 194             s->slot = s->newcodes;
 195             s->top_slot = 1 << s->cursize;
 196             fc= oc= -1;
 197         } else {
 198             code = c;
 199             if (code == s->slot && fc>=0) {
 200                 *sp++ = fc;
 201                 code = oc;
 202             }else if(code >= s->slot)
 203                 break;
 204             while (code >= s->newcodes) {
 205                 *sp++ = s->suffix[code];
 206                 code = s->prefix[code];
 207             }
 208             *sp++ = code;
 209             if (s->slot < s->top_slot && oc>=0) {
 210                 s->suffix[s->slot] = code;
 211                 s->prefix[s->slot++] = oc;
 212             }
 213             fc = code;
 214             oc = c;
 215             if (s->slot >= s->top_slot - s->extra_slot) {
 216                 if (s->cursize < LZW_MAXBITS) {
 217                     s->top_slot <<= 1;
 218                     s->curmask = mask[++s->cursize];
 219                 }
 220             }
 221         }
 222     }
 223     s->end_code = -1;
 224   the_end:
 225     s->sp = sp;
 226     s->oc = oc;
 227     s->fc = fc;
 228     return len - l;
 229 }