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ffmpeg / libavcodec / lzwenc.c @ b2755007

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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 libavcodec/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 "put_bits.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(s->maxbits >= 9 && s->maxbits <= LZW_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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    if(insize * 3 > (s->bufsize - s->output_bytes) * 2){
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        return -1;
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    }
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    if (s->last_code == 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, s->last_code);
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        if (s->tab[code].hash_prefix == LZW_PREFIX_FREE) {
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            writeCode(s, s->last_code);
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            addCode(s, c, s->last_code, code);
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            code= hash(0, c);
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        }
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        s->last_code = s->tab[code].code;
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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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    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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}