arithmetic_coding_tutorial/bitreader.h at master · danielrh/arithmetic_coding_tutorial · GitHub

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/*
 * Copyright (c) 2010 The WebM project authors. All Rights Reserved.
 *
 * Use of this source code is governed by a BSD-style license
 * that can be found in the LICENSE file in the root of the source
 * tree. An additional intellectual property rights grant can be found
 * in the file PATENTS. All contributing project authors may
 * be found in the AUTHORS file in the root of the source tree.
 */

#ifndefVPX_DSP_BITREADER_H_
#defineVPX_DSP_BITREADER_H_

#include<stddef.h>
#include<limits.h>
#include<stdint.h>
#include"./vpx_config.h"
//#include "vpx_ports/mem.h"
//#include "vpx/vp8dx.h"
//#include "vpx/vpx_integer.h"
//#include "vpx_dsp/prob.h"

#ifdef__cplusplus
extern"C" {
#endif

typedefsize_tBD_VALUE;

#defineBD_VALUE_SIZE ((int)sizeof(BD_VALUE) * CHAR_BIT)

// This is meant to be a large, positive constant that can still be efficiently
// loaded as an immediate (on platforms like ARM, for example).
// Even relatively modest values like 100 would work fine.
#defineLOTS_OF_BITS 0x40000000

typedefstruct {
// Be careful when reordering this struct, it may impact the cache negatively.
BD_VALUEvalue;
unsigned intrange;
intcount;
constuint8_t*buffer_end;
constuint8_t*buffer;
// vpx_decrypt_cb decrypt_cb;
// void *decrypt_state;
uint8_tclear_buffer[sizeof(BD_VALUE) +1];
} vpx_reader;

intvpx_reader_init(vpx_reader*r,
constuint8_t*buffer,
size_tsize);

voidvpx_reader_fill(vpx_reader*r);

constuint8_t*vpx_reader_find_end(vpx_reader*r);

staticINLINEintvpx_reader_has_error(vpx_reader*r) {
// Check if we have reached the end of the buffer.
//
// Variable 'count' stores the number of bits in the 'value' buffer, minus
// 8. The top byte is part of the algorithm, and the remainder is buffered
// to be shifted into it. So if count == 8, the top 16 bits of 'value' are
// occupied, 8 for the algorithm and 8 in the buffer.
//
// When reading a byte from the user's buffer, count is filled with 8 and
// one byte is filled into the value buffer. When we reach the end of the
// data, count is additionally filled with LOTS_OF_BITS. So when
// count == LOTS_OF_BITS - 1, the user's data has been exhausted.
//
// 1 if we have tried to decode bits after the end of stream was encountered.
// 0 No error.
returnr->count>BD_VALUE_SIZE&&r->count<LOTS_OF_BITS;
}

externintr_bitcount;

staticINLINEintvpx_read(vpx_reader*r, intprob) {
unsigned intbit=0;
BD_VALUEvalue;
BD_VALUEbigsplit;
intcount;
unsigned intrange;
unsigned intsplit= (r->range*prob+ (256-prob)) >> CHAR_BIT;

if (r->count<0)
vpx_reader_fill(r);

value=r->value;
count=r->count;

bigsplit= (BD_VALUE)split << (BD_VALUE_SIZE-CHAR_BIT);

range=split;

if (value >= bigsplit) {
range=r->range-split;
value=value-bigsplit;
bit=1;
 }

 {
conststaticuint8_tvpx_norm[256] = {
0, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
 };
 register unsigned intshift=vpx_norm[range];
range <<= shift;
value <<= shift;
count-=shift;
 }
r->value=value;
r->count=count;
r->range=range;

#ifdefDEBUG_ARICODER
//if (r_bitcount < 1000) {
fprintf(stderr, "R %d %d %d\n", r_bitcount++, prob, bit);
//}
#endif

returnbit;
}

staticINLINEintvpx_read_bit(vpx_reader*r) {
returnvpx_read(r, 128); // vpx_prob_half
}

staticINLINEintvpx_read_literal(vpx_reader*r, intbits) {
intliteral=0, bit;

for (bit=bits-1; bit >= 0; bit--)
literal |= vpx_read_bit(r) << bit;

returnliteral;
}
/*
static INLINE int vpx_read_tree(vpx_reader *r, const vpx_tree_index *tree,
 const vpx_prob *probs) {
 vpx_tree_index i = 0;

 while ((i = tree[i + vpx_read(r, probs[i >> 1])]) > 0)
 continue;

 return -i;
}
*/
#ifdef__cplusplus
} // extern "C"
#endif

#endif// VPX_DSP_BITREADER_H_