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 Libav.
   7  *
   8  * Libav 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  * Libav 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 Libav; 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
  25  * @brief LZW decoding routines
  26  * @author Fabrice Bellard
  27  * @author modified for use in TIFF by Konstantin Shishkov
  28  */
  29
  30 #include "avcodec.h"
  31 #include "lzw.h"
  32 #include "libavutil/mem.h"
  33
  34 #define LZW_MAXBITS                 12
  35 #define LZW_SIZTABLE                (1<<LZW_MAXBITS)
  36
  37 static const uint16_t mask[17] =
  38 {
  39     0x0000, 0x0001, 0x0003, 0x0007,
  40     0x000F, 0x001F, 0x003F, 0x007F,
  41     0x00FF, 0x01FF, 0x03FF, 0x07FF,
  42     0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
  43 };
  44
  45 struct LZWState {
  46     const uint8_t *buf_start, *pbuf, *ebuf;
  47     int bbits;
  48     unsigned int bbuf;
  49
  50     int mode;                   ///< Decoder mode
  51     int cursize;                ///< The current code size
  52     int curmask;
  53     int codesize;
  54     int clear_code;
  55     int end_code;
  56     int newcodes;               ///< First available code
  57     int top_slot;               ///< Highest code for current size
  58     int extra_slot;
  59     int slot;                   ///< Last read code
  60     int fc, oc;
  61     uint8_t *sp;
  62     uint8_t stack[LZW_SIZTABLE];
  63     uint8_t suffix[LZW_SIZTABLE];
  64     uint16_t prefix[LZW_SIZTABLE];
  65     int bs;                     ///< current buffer size for GIF
  66 };
  67
  68 /* get one code from stream */
  69 static int lzw_get_code(struct LZWState * s)
  70 {
  71     int c;
  72
  73     if(s->mode == FF_LZW_GIF) {
  74         while (s->bbits < s->cursize) {
  75             if (!s->bs) {
  76                 s->bs = *s->pbuf++;
  77             }
  78             s->bbuf |= (*s->pbuf++) << s->bbits;
  79             s->bbits += 8;
  80             s->bs--;
  81         }
  82         c = s->bbuf;
  83         s->bbuf >>= s->cursize;
  84     } else { // TIFF
  85         while (s->bbits < s->cursize) {
  86             s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
  87             s->bbits += 8;
  88         }
  89         c = s->bbuf >> (s->bbits - s->cursize);
  90     }
  91     s->bbits -= s->cursize;
  92     return c & s->curmask;
  93 }
  94
  95 int ff_lzw_size_read(LZWState *p)
  96 {
  97     struct LZWState *s = p;
  98     return s->pbuf - s->buf_start;
  99 }
 100
 101 void ff_lzw_decode_tail(LZWState *p)
 102 {
 103     struct LZWState *s = (struct LZWState *)p;
 104
 105     if(s->mode == FF_LZW_GIF) {
 106         while (s->bs > 0) {
 107             if (s->bs >= s->ebuf - s->pbuf) {
 108                 s->pbuf = s->ebuf;
 109                 break;
 110             } else {
 111                 s->pbuf += s->bs;
 112                 s->bs = *s->pbuf++;
 113             }
 114         }
 115     }else
 116         s->pbuf= s->ebuf;
 117 }
 118
 119 av_cold void ff_lzw_decode_open(LZWState **p)
 120 {
 121     *p = av_mallocz(sizeof(struct LZWState));
 122 }
 123
 124 av_cold void ff_lzw_decode_close(LZWState **p)
 125 {
 126     av_freep(p);
 127 }
 128
 129 /**
 130  * Initialize LZW decoder
 131  * @param p LZW context
 132  * @param csize initial code size in bits
 133  * @param buf input data
 134  * @param buf_size input data size
 135  * @param mode decoder working mode - either GIF or TIFF
 136  */
 137 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
 138 {
 139     struct LZWState *s = (struct LZWState *)p;
 140
 141     if(csize < 1 || csize >= LZW_MAXBITS)
 142         return -1;
 143     /* read buffer */
 144     s->pbuf = buf;
 145     s->ebuf = s->pbuf + buf_size;
 146     s->bbuf = 0;
 147     s->bbits = 0;
 148     s->bs = 0;
 149
 150     /* decoder */
 151     s->codesize = csize;
 152     s->cursize = s->codesize + 1;
 153     s->curmask = mask[s->cursize];
 154     s->top_slot = 1 << s->cursize;
 155     s->clear_code = 1 << s->codesize;
 156     s->end_code = s->clear_code + 1;
 157     s->slot = s->newcodes = s->clear_code + 2;
 158     s->oc = s->fc = -1;
 159     s->sp = s->stack;
 160
 161     s->mode = mode;
 162     s->extra_slot = s->mode == FF_LZW_TIFF;
 163     return 0;
 164 }
 165
 166 /**
 167  * Decode given number of bytes
 168  * NOTE: the algorithm here is inspired from the LZW GIF decoder
 169  *  written by Steven A. Bennett in 1987.
 170  *
 171  * @param p LZW context
 172  * @param buf output buffer
 173  * @param len number of bytes to decode
 174  * @return number of bytes decoded
 175  */
 176 int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
 177     int l, c, code, oc, fc;
 178     uint8_t *sp;
 179     struct LZWState *s = (struct LZWState *)p;
 180
 181     if (s->end_code < 0)
 182         return 0;
 183
 184     l = len;
 185     sp = s->sp;
 186     oc = s->oc;
 187     fc = s->fc;
 188
 189     for (;;) {
 190         while (sp > s->stack) {
 191             *buf++ = *(--sp);
 192             if ((--l) == 0)
 193                 goto the_end;
 194         }
 195         c = lzw_get_code(s);
 196         if (c == s->end_code) {
 197             break;
 198         } else if (c == s->clear_code) {
 199             s->cursize = s->codesize + 1;
 200             s->curmask = mask[s->cursize];
 201             s->slot = s->newcodes;
 202             s->top_slot = 1 << s->cursize;
 203             fc= oc= -1;
 204         } else {
 205             code = c;
 206             if (code == s->slot && fc>=0) {
 207                 *sp++ = fc;
 208                 code = oc;
 209             }else if(code >= s->slot)
 210                 break;
 211             while (code >= s->newcodes) {
 212                 *sp++ = s->suffix[code];
 213                 code = s->prefix[code];
 214             }
 215             *sp++ = code;
 216             if (s->slot < s->top_slot && oc>=0) {
 217                 s->suffix[s->slot] = code;
 218                 s->prefix[s->slot++] = oc;
 219             }
 220             fc = code;
 221             oc = c;
 222             if (s->slot >= s->top_slot - s->extra_slot) {
 223                 if (s->cursize < LZW_MAXBITS) {
 224                     s->top_slot <<= 1;
 225                     s->curmask = mask[++s->cursize];
 226                 }
 227             }
 228         }
 229     }
 230     s->end_code = -1;
 231   the_end:
 232     s->sp = sp;
 233     s->oc = oc;
 234     s->fc = fc;
 235     return len - l;
 236 }