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libavcodec/lzw.c

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00001 /*
00002  * LZW decoder
00003  * Copyright (c) 2003 Fabrice Bellard
00004  * Copyright (c) 2006 Konstantin Shishkov
00005  *
00006  * This file is part of FFmpeg.
00007  *
00008  * FFmpeg is free software; you can redistribute it and/or
00009  * modify it under the terms of the GNU Lesser General Public
00010  * License as published by the Free Software Foundation; either
00011  * version 2.1 of the License, or (at your option) any later version.
00012  *
00013  * FFmpeg is distributed in the hope that it will be useful,
00014  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00015  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00016  * Lesser General Public License for more details.
00017  *
00018  * You should have received a copy of the GNU Lesser General Public
00019  * License along with FFmpeg; if not, write to the Free Software
00020  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00021  */
00022 
00030 #include "avcodec.h"
00031 #include "lzw.h"
00032 
00033 #define LZW_MAXBITS                 12
00034 #define LZW_SIZTABLE                (1<<LZW_MAXBITS)
00035 
00036 static const uint16_t mask[17] =
00037 {
00038     0x0000, 0x0001, 0x0003, 0x0007,
00039     0x000F, 0x001F, 0x003F, 0x007F,
00040     0x00FF, 0x01FF, 0x03FF, 0x07FF,
00041     0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
00042 };
00043 
00044 struct LZWState {
00045     const uint8_t *pbuf, *ebuf;
00046     int bbits;
00047     unsigned int bbuf;
00048 
00049     int mode;                   
00050     int cursize;                
00051     int curmask;
00052     int codesize;
00053     int clear_code;
00054     int end_code;
00055     int newcodes;               
00056     int top_slot;               
00057     int extra_slot;
00058     int slot;                   
00059     int fc, oc;
00060     uint8_t *sp;
00061     uint8_t stack[LZW_SIZTABLE];
00062     uint8_t suffix[LZW_SIZTABLE];
00063     uint16_t prefix[LZW_SIZTABLE];
00064     int bs;                     
00065 };
00066 
00067 /* get one code from stream */
00068 static int lzw_get_code(struct LZWState * s)
00069 {
00070     int c;
00071 
00072     if(s->mode == FF_LZW_GIF) {
00073         while (s->bbits < s->cursize) {
00074             if (!s->bs) {
00075                 s->bs = *s->pbuf++;
00076             }
00077             s->bbuf |= (*s->pbuf++) << s->bbits;
00078             s->bbits += 8;
00079             s->bs--;
00080         }
00081         c = s->bbuf;
00082         s->bbuf >>= s->cursize;
00083     } else { // TIFF
00084         while (s->bbits < s->cursize) {
00085             s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
00086             s->bbits += 8;
00087         }
00088         c = s->bbuf >> (s->bbits - s->cursize);
00089     }
00090     s->bbits -= s->cursize;
00091     return c & s->curmask;
00092 }
00093 
00094 const uint8_t* ff_lzw_cur_ptr(LZWState *p)
00095 {
00096     return ((struct LZWState*)p)->pbuf;
00097 }
00098 
00099 void ff_lzw_decode_tail(LZWState *p)
00100 {
00101     struct LZWState *s = (struct LZWState *)p;
00102 
00103     if(s->mode == FF_LZW_GIF) {
00104         while(s->pbuf < s->ebuf && s->bs>0){
00105             s->pbuf += s->bs;
00106             s->bs = *s->pbuf++;
00107         }
00108     }else
00109         s->pbuf= s->ebuf;
00110 }
00111 
00112 av_cold void ff_lzw_decode_open(LZWState **p)
00113 {
00114     *p = av_mallocz(sizeof(struct LZWState));
00115 }
00116 
00117 av_cold void ff_lzw_decode_close(LZWState **p)
00118 {
00119     av_freep(p);
00120 }
00121 
00130 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
00131 {
00132     struct LZWState *s = (struct LZWState *)p;
00133 
00134     if(csize < 1 || csize >= LZW_MAXBITS)
00135         return -1;
00136     /* read buffer */
00137     s->pbuf = buf;
00138     s->ebuf = s->pbuf + buf_size;
00139     s->bbuf = 0;
00140     s->bbits = 0;
00141     s->bs = 0;
00142 
00143     /* decoder */
00144     s->codesize = csize;
00145     s->cursize = s->codesize + 1;
00146     s->curmask = mask[s->cursize];
00147     s->top_slot = 1 << s->cursize;
00148     s->clear_code = 1 << s->codesize;
00149     s->end_code = s->clear_code + 1;
00150     s->slot = s->newcodes = s->clear_code + 2;
00151     s->oc = s->fc = -1;
00152     s->sp = s->stack;
00153 
00154     s->mode = mode;
00155     s->extra_slot = s->mode == FF_LZW_TIFF;
00156     return 0;
00157 }
00158 
00169 int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
00170     int l, c, code, oc, fc;
00171     uint8_t *sp;
00172     struct LZWState *s = (struct LZWState *)p;
00173 
00174     if (s->end_code < 0)
00175         return 0;
00176 
00177     l = len;
00178     sp = s->sp;
00179     oc = s->oc;
00180     fc = s->fc;
00181 
00182     for (;;) {
00183         while (sp > s->stack) {
00184             *buf++ = *(--sp);
00185             if ((--l) == 0)
00186                 goto the_end;
00187         }
00188         c = lzw_get_code(s);
00189         if (c == s->end_code) {
00190             break;
00191         } else if (c == s->clear_code) {
00192             s->cursize = s->codesize + 1;
00193             s->curmask = mask[s->cursize];
00194             s->slot = s->newcodes;
00195             s->top_slot = 1 << s->cursize;
00196             fc= oc= -1;
00197         } else {
00198             code = c;
00199             if (code == s->slot && fc>=0) {
00200                 *sp++ = fc;
00201                 code = oc;
00202             }else if(code >= s->slot)
00203                 break;
00204             while (code >= s->newcodes) {
00205                 *sp++ = s->suffix[code];
00206                 code = s->prefix[code];
00207             }
00208             *sp++ = code;
00209             if (s->slot < s->top_slot && oc>=0) {
00210                 s->suffix[s->slot] = code;
00211                 s->prefix[s->slot++] = oc;
00212             }
00213             fc = code;
00214             oc = c;
00215             if (s->slot >= s->top_slot - s->extra_slot) {
00216                 if (s->cursize < LZW_MAXBITS) {
00217                     s->top_slot <<= 1;
00218                     s->curmask = mask[++s->cursize];
00219                 }
00220             }
00221         }
00222     }
00223     s->end_code = -1;
00224   the_end:
00225     s->sp = sp;
00226     s->oc = oc;
00227     s->fc = fc;
00228     return len - l;
00229 }

Generated on Fri Sep 16 2011 17:17:39 for FFmpeg by  doxygen 1.7.1