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/*
* LZW encoder
* Copyright (c) 2007 Bartlomiej Wolowiec
*
* 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
* LZW encoder
* @author Bartlomiej Wolowiec
*/
#include "avcodec.h"
#include "put_bits.h"
#include "lzw.h"
#define LZW_MAXBITS 12
#define LZW_SIZTABLE (1<<LZW_MAXBITS)
#define LZW_HASH_SIZE 16411
#define LZW_HASH_SHIFT 6
#define LZW_PREFIX_EMPTY -1
#define LZW_PREFIX_FREE -2
/** One code in hash table */
typedef struct Code{
/// Hash code of prefix, LZW_PREFIX_EMPTY if empty prefix, or LZW_PREFIX_FREE if no code
int hash_prefix;
int code; ///< LZW code
uint8_t suffix; ///< Last character in code block
}Code;
/** LZW encode state */
typedef struct LZWEncodeState {
int clear_code; ///< Value of clear code
int end_code; ///< Value of end code
Code tab[LZW_HASH_SIZE]; ///< Hash table
int tabsize; ///< Number of values in hash table
int bits; ///< Actual bits code
int bufsize; ///< Size of output buffer
PutBitContext pb; ///< Put bit context for output
int maxbits; ///< Max bits code
int maxcode; ///< Max value of code
int output_bytes; ///< Number of written bytes
int last_code; ///< Value of last output code or LZW_PREFIX_EMPTY
enum FF_LZW_MODES mode; ///< TIFF or GIF
void (*put_bits)(PutBitContext *, int, unsigned); ///< GIF is LE while TIFF is BE
}LZWEncodeState;
const int ff_lzw_encode_state_size = sizeof(LZWEncodeState);
/**
* Hash function adding character
* @param head LZW code for prefix
* @param add Character to add
* @return New hash value
*/
static inline int hash(int head, const int add)
{
head ^= (add << LZW_HASH_SHIFT);
if (head >= LZW_HASH_SIZE)
head -= LZW_HASH_SIZE;
assert(head >= 0 && head < LZW_HASH_SIZE);
return head;
}
/**
* Hash function calculates next hash value
* @param head Actual hash code
* @param offset Offset calculated by hashOffset
* @return New hash value
*/
static inline int hashNext(int head, const int offset)
{
head -= offset;
if(head < 0)
head += LZW_HASH_SIZE;
return head;
}
/**
* Hash function calculates hash offset
* @param head Actual hash code
* @return Hash offset
*/
static inline int hashOffset(const int head)
{
return head ? LZW_HASH_SIZE - head : 1;
}
/**
* Write one code to stream
* @param s LZW state
* @param c code to write
*/
static inline void writeCode(LZWEncodeState * s, int c)
{
assert(0 <= c && c < 1 << s->bits);
s->put_bits(&s->pb, s->bits, c);
}
/**
* Find LZW code for block
* @param s LZW state
* @param c Last character in block
* @param hash_prefix LZW code for prefix
* @return LZW code for block or -1 if not found in table
*/
static inline int findCode(LZWEncodeState * s, uint8_t c, int hash_prefix)
{
int h = hash(FFMAX(hash_prefix, 0), c);
int hash_offset = hashOffset(h);
while (s->tab[h].hash_prefix != LZW_PREFIX_FREE) {
if ((s->tab[h].suffix == c)
&& (s->tab[h].hash_prefix == hash_prefix))
return h;
h = hashNext(h, hash_offset);
}
return h;
}
/**
* Add block to LZW code table
* @param s LZW state
* @param c Last character in block
* @param hash_prefix LZW code for prefix
* @param hash_code LZW code for bytes block
*/
static inline void addCode(LZWEncodeState * s, uint8_t c, int hash_prefix, int hash_code)
{
s->tab[hash_code].code = s->tabsize;
s->tab[hash_code].suffix = c;
s->tab[hash_code].hash_prefix = hash_prefix;
s->tabsize++;
if (s->tabsize >= (1 << s->bits) + (s->mode == FF_LZW_GIF))
s->bits++;
}
/**
* Clear LZW code table
* @param s LZW state
*/
static void clearTable(LZWEncodeState * s)
{
int i, h;
writeCode(s, s->clear_code);
s->bits = 9;
for (i = 0; i < LZW_HASH_SIZE; i++) {
s->tab[i].hash_prefix = LZW_PREFIX_FREE;
}
for (i = 0; i < 256; i++) {
h = hash(0, i);
s->tab[h].code = i;
s->tab[h].suffix = i;
s->tab[h].hash_prefix = LZW_PREFIX_EMPTY;
}
s->tabsize = 258;
}
/**
* Calculate number of bytes written
* @param s LZW encode state
* @return Number of bytes written
*/
static int writtenBytes(LZWEncodeState *s){
int ret = put_bits_count(&s->pb) >> 3;
ret -= s->output_bytes;
s->output_bytes += ret;
return ret;
}
/**
* Initialize LZW encoder. Please set s->clear_code, s->end_code and s->maxbits before run.
* @param s LZW state
* @param outbuf Output buffer
* @param outsize Size of output buffer
* @param maxbits Maximum length of code
*/
void ff_lzw_encode_init(LZWEncodeState *s, uint8_t *outbuf, int outsize,
int maxbits, enum FF_LZW_MODES mode,
void (*lzw_put_bits)(PutBitContext *, int, unsigned))
{
s->clear_code = 256;
s->end_code = 257;
s->maxbits = maxbits;
init_put_bits(&s->pb, outbuf, outsize);
s->bufsize = outsize;
assert(s->maxbits >= 9 && s->maxbits <= LZW_MAXBITS);
s->maxcode = 1 << s->maxbits;
s->output_bytes = 0;
s->last_code = LZW_PREFIX_EMPTY;
s->bits = 9;
s->mode = mode;
s->put_bits = lzw_put_bits;
}
/**
* LZW main compress function
* @param s LZW state
* @param inbuf Input buffer
* @param insize Size of input buffer
* @return Number of bytes written or -1 on error
*/
int ff_lzw_encode(LZWEncodeState * s, const uint8_t * inbuf, int insize)
{
int i;
if(insize * 3 > (s->bufsize - s->output_bytes) * 2){
return -1;
}
if (s->last_code == LZW_PREFIX_EMPTY)
clearTable(s);
for (i = 0; i < insize; i++) {
uint8_t c = *inbuf++;
int code = findCode(s, c, s->last_code);
if (s->tab[code].hash_prefix == LZW_PREFIX_FREE) {
writeCode(s, s->last_code);
addCode(s, c, s->last_code, code);
code= hash(0, c);
}
s->last_code = s->tab[code].code;
if (s->tabsize >= s->maxcode - 1) {
clearTable(s);
}
}
return writtenBytes(s);
}
/**
* Write end code and flush bitstream
* @param s LZW state
* @return Number of bytes written or -1 on error
*/
int ff_lzw_encode_flush(LZWEncodeState *s,
void (*lzw_flush_put_bits)(PutBitContext *))
{
if (s->last_code != -1)
writeCode(s, s->last_code);
writeCode(s, s->end_code);
lzw_flush_put_bits(&s->pb);
s->last_code = -1;
return writtenBytes(s);
}
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