/* * LZW decoder * Copyright (c) 2003 Fabrice Bellard * Copyright (c) 2006 Konstantin Shishkov * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ /** * @file libavcodec/lzw.c * @brief LZW decoding routines * @author Fabrice Bellard * Modified for use in TIFF by Konstantin Shishkov */ #include "avcodec.h" #include "lzw.h" #define LZW_MAXBITS 12 #define LZW_SIZTABLE (1<<LZW_MAXBITS) static const uint16_t mask[17] = { 0x0000, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF }; struct LZWState { const uint8_t *pbuf, *ebuf; int bbits; unsigned int bbuf; int mode; ///< Decoder mode int cursize; ///< The current code size int curmask; int codesize; int clear_code; int end_code; int newcodes; ///< First available code int top_slot; ///< Highest code for current size int extra_slot; int slot; ///< Last read code int fc, oc; uint8_t *sp; uint8_t stack[LZW_SIZTABLE]; uint8_t suffix[LZW_SIZTABLE]; uint16_t prefix[LZW_SIZTABLE]; int bs; ///< current buffer size for GIF }; /* get one code from stream */ static int lzw_get_code(struct LZWState * s) { int c; if(s->mode == FF_LZW_GIF) { while (s->bbits < s->cursize) { if (!s->bs) { s->bs = *s->pbuf++; } s->bbuf |= (*s->pbuf++) << s->bbits; s->bbits += 8; s->bs--; } c = s->bbuf; s->bbuf >>= s->cursize; } else { // TIFF while (s->bbits < s->cursize) { s->bbuf = (s->bbuf << 8) | (*s->pbuf++); s->bbits += 8; } c = s->bbuf >> (s->bbits - s->cursize); } s->bbits -= s->cursize; return c & s->curmask; } const uint8_t* ff_lzw_cur_ptr(LZWState *p) { return ((struct LZWState*)p)->pbuf; } void ff_lzw_decode_tail(LZWState *p) { struct LZWState *s = (struct LZWState *)p; if(s->mode == FF_LZW_GIF) { while(s->pbuf < s->ebuf && s->bs>0){ s->pbuf += s->bs; s->bs = *s->pbuf++; } }else s->pbuf= s->ebuf; } av_cold void ff_lzw_decode_open(LZWState **p) { *p = av_mallocz(sizeof(struct LZWState)); } av_cold void ff_lzw_decode_close(LZWState **p) { av_freep(p); } /** * Initialize LZW decoder * @param s LZW context * @param csize initial code size in bits * @param buf input data * @param buf_size input data size * @param mode decoder working mode - either GIF or TIFF */ int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode) { struct LZWState *s = (struct LZWState *)p; if(csize < 1 || csize >= LZW_MAXBITS) return -1; /* read buffer */ s->pbuf = buf; s->ebuf = s->pbuf + buf_size; s->bbuf = 0; s->bbits = 0; s->bs = 0; /* decoder */ s->codesize = csize; s->cursize = s->codesize + 1; s->curmask = mask[s->cursize]; s->top_slot = 1 << s->cursize; s->clear_code = 1 << s->codesize; s->end_code = s->clear_code + 1; s->slot = s->newcodes = s->clear_code + 2; s->oc = s->fc = -1; s->sp = s->stack; s->mode = mode; s->extra_slot = s->mode == FF_LZW_TIFF; return 0; } /** * Decode given number of bytes * NOTE: the algorithm here is inspired from the LZW GIF decoder * written by Steven A. Bennett in 1987. * * @param s LZW context * @param buf output buffer * @param len number of bytes to decode * @return number of bytes decoded */ int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){ int l, c, code, oc, fc; uint8_t *sp; struct LZWState *s = (struct LZWState *)p; if (s->end_code < 0) return 0; l = len; sp = s->sp; oc = s->oc; fc = s->fc; for (;;) { while (sp > s->stack) { *buf++ = *(--sp); if ((--l) == 0) goto the_end; } c = lzw_get_code(s); if (c == s->end_code) { break; } else if (c == s->clear_code) { s->cursize = s->codesize + 1; s->curmask = mask[s->cursize]; s->slot = s->newcodes; s->top_slot = 1 << s->cursize; fc= oc= -1; } else { code = c; if (code == s->slot && fc>=0) { *sp++ = fc; code = oc; }else if(code >= s->slot) break; while (code >= s->newcodes) { *sp++ = s->suffix[code]; code = s->prefix[code]; } *sp++ = code; if (s->slot < s->top_slot && oc>=0) { s->suffix[s->slot] = code; s->prefix[s->slot++] = oc; } fc = code; oc = c; if (s->slot >= s->top_slot - s->extra_slot) { if (s->cursize < LZW_MAXBITS) { s->top_slot <<= 1; s->curmask = mask[++s->cursize]; } } } } s->end_code = -1; the_end: s->sp = sp; s->oc = oc; s->fc = fc; return len - l; }