mirror of https://github.com/FFmpeg/FFmpeg.git
Originally committed as revision 8644 to svn://svn.ffmpeg.org/ffmpeg/trunkpull/126/head
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/*
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* LZW encoder |
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* Copyright (c) 2007 Bartlomiej Wolowiec |
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* |
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* This file is part of FFmpeg. |
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* |
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* FFmpeg is free software; you can redistribute it and/or |
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* modify it under the terms of the GNU Lesser General Public |
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* License as published by the Free Software Foundation; either |
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* version 2.1 of the License, or (at your option) any later version. |
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* |
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* FFmpeg is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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* Lesser General Public License for more details. |
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* |
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* You should have received a copy of the GNU Lesser General Public |
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* License along with FFmpeg; if not, write to the Free Software |
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
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*/ |
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/**
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* LZW encoder |
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* @file lzwenc.c |
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* @author Bartlomiej Wolowiec |
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*/ |
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#include "avcodec.h" |
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#include "bitstream.h" |
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#include "lzw.h" |
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#define LZW_MAXBITS 12 |
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#define LZW_SIZTABLE (1<<LZW_MAXBITS) |
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#define LZW_HASH_SIZE 16411 |
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#define LZW_HASH_SHIFT 6 |
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#define LZW_PREFIX_EMPTY -1 |
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#define LZW_PREFIX_FREE -2 |
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/** One code in hash table */ |
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typedef struct Code{ |
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/// Hash code of prefix, LZW_PREFIX_EMPTY if empty prefix, or LZW_PREFIX_FREE if no code
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int hash_prefix; |
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int code; ///< LZW code
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uint8_t suffix; ///< Last character in code block
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}Code; |
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/** LZW encode state */ |
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typedef struct LZWEncodeState { |
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int clear_code; ///< Value of clear code
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int end_code; ///< Value of end code
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Code tab[LZW_HASH_SIZE]; ///< Hash table
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int tabsize; ///< Number of values in hash table
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int bits; ///< Actual bits code
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int bufsize; ///< Size of output buffer
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PutBitContext pb; ///< Put bit context for output
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int maxbits; ///< Max bits code
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int maxcode; ///< Max value of code
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int output_bytes; ///< Number of written bytes
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int last_code; ///< Value of last output code or LZW_PREFIX_EMPTY
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}LZWEncodeState; |
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const int ff_lzw_encode_state_size = sizeof(LZWEncodeState); |
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/**
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* Hash function adding character |
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* @param head LZW code for prefix |
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* @param add Character to add |
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* @return New hash value |
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*/ |
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static inline int hash(int head, const int add) |
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{ |
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head ^= (add << LZW_HASH_SHIFT); |
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if (head >= LZW_HASH_SIZE) |
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head -= LZW_HASH_SIZE; |
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assert(head >= 0 && head < LZW_HASH_SIZE); |
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return head; |
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} |
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/**
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* Hash function calculates next hash value |
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* @param head Actual hash code |
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* @param offset Offset calculated by hashOffset |
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* @return New hash value |
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*/ |
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static inline int hashNext(int head, const int offset) |
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{ |
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head -= offset; |
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if(head < 0) |
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head += LZW_HASH_SIZE; |
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return head; |
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} |
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/**
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* Hash function calculates hash offset |
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* @param head Actual hash code |
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* @return Hash offset |
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*/ |
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static inline int hashOffset(const int head) |
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{ |
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return head ? LZW_HASH_SIZE - head : 1; |
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} |
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/**
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* Write one code to stream |
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* @param s LZW state |
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* @param c code to write |
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*/ |
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static inline void writeCode(LZWEncodeState * s, int c) |
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{ |
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assert(0 <= c && c < 1 << s->bits); |
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put_bits(&s->pb, s->bits, c); |
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} |
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/**
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* Find LZW code for block |
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* @param s LZW state |
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* @param c Last character in block |
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* @param hash_prefix LZW code for prefix |
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* @return LZW code for block or -1 if not found in table |
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*/ |
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static inline int findCode(LZWEncodeState * s, uint8_t c, int hash_prefix) |
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{ |
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int h = hash(FFMAX(hash_prefix, 0), c); |
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int hash_offset = hashOffset(h); |
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while (s->tab[h].hash_prefix != LZW_PREFIX_FREE) { |
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if ((s->tab[h].suffix == c) |
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&& (s->tab[h].hash_prefix == hash_prefix)) |
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return h; |
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h = hashNext(h, hash_offset); |
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} |
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return h; |
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} |
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/**
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* Add block to LZW code table |
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* @param s LZW state |
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* @param c Last character in block |
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* @param hash_prefix LZW code for prefix |
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* @param hash_code LZW code for bytes block |
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*/ |
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static inline void addCode(LZWEncodeState * s, uint8_t c, int hash_prefix, int hash_code) |
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{ |
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s->tab[hash_code].code = s->tabsize; |
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s->tab[hash_code].suffix = c; |
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s->tab[hash_code].hash_prefix = hash_prefix; |
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s->tabsize++; |
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if (s->tabsize >= 1 << s->bits) |
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s->bits++; |
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} |
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/**
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* Clear LZW code table |
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* @param s LZW state |
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*/ |
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static void clearTable(LZWEncodeState * s) |
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{ |
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int i, h; |
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writeCode(s, s->clear_code); |
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s->bits = 9; |
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for (i = 0; i < LZW_HASH_SIZE; i++) { |
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s->tab[i].hash_prefix = LZW_PREFIX_FREE; |
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} |
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for (i = 0; i < 256; i++) { |
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h = hash(0, i); |
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s->tab[h].code = i; |
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s->tab[h].suffix = i; |
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s->tab[h].hash_prefix = LZW_PREFIX_EMPTY; |
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} |
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s->tabsize = 258; |
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} |
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/**
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* Calculate number of bytes written |
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* @param s LZW encode state |
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* @return Number of bytes written |
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*/ |
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static int writtenBytes(LZWEncodeState *s){ |
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int ret = (put_bits_count(&s->pb)) >> 3; |
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ret -= s->output_bytes; |
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s->output_bytes += ret; |
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return ret; |
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} |
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/**
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* Initialize LZW encoder. Please set s->clear_code, s->end_code and s->maxbits before run. |
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* @param s LZW state |
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* @param outbuf Output buffer |
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* @param outsize Size of output buffer |
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* @param maxbits Maximum length of code |
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*/ |
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void ff_lzw_encode_init(LZWEncodeState * s, uint8_t * outbuf, int outsize, int maxbits) |
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{ |
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s->clear_code = 256; |
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s->end_code = 257; |
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s->maxbits = maxbits; |
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init_put_bits(&s->pb, outbuf, outsize); |
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s->bufsize = outsize; |
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assert(9 <= s->maxbits && s->maxbits <= s->maxbits); |
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s->maxcode = 1 << s->maxbits; |
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s->output_bytes = 0; |
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s->last_code = LZW_PREFIX_EMPTY; |
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s->bits = 9; |
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} |
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/**
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* LZW main compress function |
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* @param s LZW state |
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* @param inbuf Input buffer |
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* @param insize Size of input buffer |
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* @return Number of bytes written or -1 on error |
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*/ |
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int ff_lzw_encode(LZWEncodeState * s, const uint8_t * inbuf, int insize) |
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{ |
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int i; |
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int code_prefix = s->last_code; |
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if(insize * 3 > (s->bufsize - s->output_bytes) * 2){ |
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return -1; |
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} |
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if (code_prefix == LZW_PREFIX_EMPTY) |
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clearTable(s); |
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for (i = 0; i < insize; i++) { |
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uint8_t c = *inbuf++; |
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int code = findCode(s, c, code_prefix); |
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if (s->tab[code].hash_prefix != LZW_PREFIX_FREE) { |
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code_prefix = s->tab[code].code; |
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} else { |
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writeCode(s, code_prefix); |
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addCode(s, c, code_prefix, code); |
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code_prefix = s->tab[hash(0, c)].code; |
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} |
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if (s->tabsize >= s->maxcode - 1) { |
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clearTable(s); |
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} |
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} |
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s->last_code = code_prefix; |
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return writtenBytes(s); |
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} |
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/**
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* Write end code and flush bitstream |
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* @param s LZW state |
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* @return Number of bytes written or -1 on error |
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*/ |
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int ff_lzw_encode_flush(LZWEncodeState * s) |
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{ |
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if (s->last_code != -1) |
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writeCode(s, s->last_code); |
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writeCode(s, s->end_code); |
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flush_put_bits(&s->pb); |
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s->last_code = -1; |
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return writtenBytes(s); |
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} |
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