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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 Libav.
00007  *
00008  * Libav 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  * Libav 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 Libav; 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->bs > 0) {
00105             if (s->pbuf + s->bs >= s->ebuf) {
00106                 s->pbuf = s->ebuf;
00107                 break;
00108             } else {
00109                 s->pbuf += s->bs;
00110                 s->bs = *s->pbuf++;
00111             }
00112         }
00113     }else
00114         s->pbuf= s->ebuf;
00115 }
00116 
00117 av_cold void ff_lzw_decode_open(LZWState **p)
00118 {
00119     *p = av_mallocz(sizeof(struct LZWState));
00120 }
00121 
00122 av_cold void ff_lzw_decode_close(LZWState **p)
00123 {
00124     av_freep(p);
00125 }
00126 
00135 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
00136 {
00137     struct LZWState *s = (struct LZWState *)p;
00138 
00139     if(csize < 1 || csize >= LZW_MAXBITS)
00140         return -1;
00141     /* read buffer */
00142     s->pbuf = buf;
00143     s->ebuf = s->pbuf + buf_size;
00144     s->bbuf = 0;
00145     s->bbits = 0;
00146     s->bs = 0;
00147 
00148     /* decoder */
00149     s->codesize = csize;
00150     s->cursize = s->codesize + 1;
00151     s->curmask = mask[s->cursize];
00152     s->top_slot = 1 << s->cursize;
00153     s->clear_code = 1 << s->codesize;
00154     s->end_code = s->clear_code + 1;
00155     s->slot = s->newcodes = s->clear_code + 2;
00156     s->oc = s->fc = -1;
00157     s->sp = s->stack;
00158 
00159     s->mode = mode;
00160     s->extra_slot = s->mode == FF_LZW_TIFF;
00161     return 0;
00162 }
00163 
00174 int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
00175     int l, c, code, oc, fc;
00176     uint8_t *sp;
00177     struct LZWState *s = (struct LZWState *)p;
00178 
00179     if (s->end_code < 0)
00180         return 0;
00181 
00182     l = len;
00183     sp = s->sp;
00184     oc = s->oc;
00185     fc = s->fc;
00186 
00187     for (;;) {
00188         while (sp > s->stack) {
00189             *buf++ = *(--sp);
00190             if ((--l) == 0)
00191                 goto the_end;
00192         }
00193         c = lzw_get_code(s);
00194         if (c == s->end_code) {
00195             break;
00196         } else if (c == s->clear_code) {
00197             s->cursize = s->codesize + 1;
00198             s->curmask = mask[s->cursize];
00199             s->slot = s->newcodes;
00200             s->top_slot = 1 << s->cursize;
00201             fc= oc= -1;
00202         } else {
00203             code = c;
00204             if (code == s->slot && fc>=0) {
00205                 *sp++ = fc;
00206                 code = oc;
00207             }else if(code >= s->slot)
00208                 break;
00209             while (code >= s->newcodes) {
00210                 *sp++ = s->suffix[code];
00211                 code = s->prefix[code];
00212             }
00213             *sp++ = code;
00214             if (s->slot < s->top_slot && oc>=0) {
00215                 s->suffix[s->slot] = code;
00216                 s->prefix[s->slot++] = oc;
00217             }
00218             fc = code;
00219             oc = c;
00220             if (s->slot >= s->top_slot - s->extra_slot) {
00221                 if (s->cursize < LZW_MAXBITS) {
00222                     s->top_slot <<= 1;
00223                     s->curmask = mask[++s->cursize];
00224                 }
00225             }
00226         }
00227     }
00228     s->end_code = -1;
00229   the_end:
00230     s->sp = sp;
00231     s->oc = oc;
00232     s->fc = fc;
00233     return len - l;
00234 }
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