range_decoder.h

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//
//  Authors:    Igor Pavlov
//              Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
 
#ifndef LZMA_RANGE_DECODER_H
#define LZMA_RANGE_DECODER_H
 
#include "range_common.h"
 
 
typedef struct {
    uint32_t range;
    uint32_t code;
    uint32_t init_bytes_left;
} lzma_range_decoder;
 
 
static inline lzma_ret
rc_read_init(lzma_range_decoder *rc, const uint8_t *restrict in,
        size_t *restrict in_pos, size_t in_size)
{
    while (rc->init_bytes_left > 0) {
        if (*in_pos == in_size)
            return LZMA_OK;
 
        // The first byte is always 0x00. It could have been omitted
        // in LZMA2 but it wasn't, so one byte is wasted in every
        // LZMA2 chunk.
        if (rc->init_bytes_left == 5 && in[*in_pos] != 0x00)
            return LZMA_DATA_ERROR;
 
        rc->code = (rc->code << 8) | in[*in_pos];
        ++*in_pos;
        --rc->init_bytes_left;
    }
 
    return LZMA_STREAM_END;
}
 
 
#define rc_to_local(range_decoder, in_pos) \
    lzma_range_decoder rc = range_decoder; \
    size_t rc_in_pos = (in_pos); \
    uint32_t rc_bound
 
 
#define rc_from_local(range_decoder, in_pos) \
do { \
    range_decoder = rc; \
    in_pos = rc_in_pos; \
} while (0)
 
 
#define rc_reset(range_decoder) \
do { \
    (range_decoder).range = UINT32_MAX; \
    (range_decoder).code = 0; \
    (range_decoder).init_bytes_left = 5; \
} while (0)
 
 
#define rc_is_finished(range_decoder) \
    ((range_decoder).code == 0)
 
 
#define rc_normalize(seq) \
do { \
    if (rc.range < RC_TOP_VALUE) { \
        if (unlikely(rc_in_pos == in_size)) { \
            coder->sequence = seq; \
            goto out; \
        } \
        rc.range <<= RC_SHIFT_BITS; \
        rc.code = (rc.code << RC_SHIFT_BITS) | in[rc_in_pos++]; \
    } \
} while (0)
 
 
#define rc_if_0(prob, seq) \
    rc_normalize(seq); \
    rc_bound = (rc.range >> RC_BIT_MODEL_TOTAL_BITS) * (prob); \
    if (rc.code < rc_bound)
 
 
#define rc_update_0(prob) \
do { \
    rc.range = rc_bound; \
    prob += (RC_BIT_MODEL_TOTAL - (prob)) >> RC_MOVE_BITS; \
} while (0)
 
 
#define rc_update_1(prob) \
do { \
    rc.range -= rc_bound; \
    rc.code -= rc_bound; \
    prob -= (prob) >> RC_MOVE_BITS; \
} while (0)
 
 
#define rc_bit_last(prob, action0, action1, seq) \
do { \
    rc_if_0(prob, seq) { \
        rc_update_0(prob); \
        action0; \
    } else { \
        rc_update_1(prob); \
        action1; \
    } \
} while (0)
 
 
#define rc_bit(prob, action0, action1, seq) \
    rc_bit_last(prob, \
        symbol <<= 1; action0, \
        symbol = (symbol << 1) + 1; action1, \
        seq);
 
 
#define rc_bit_case(prob, action0, action1, seq) \
    case seq: rc_bit(prob, action0, action1, seq)
 
 
#define rc_direct(dest, seq) \
do { \
    rc_normalize(seq); \
    rc.range >>= 1; \
    rc.code -= rc.range; \
    rc_bound = UINT32_C(0) - (rc.code >> 31); \
    rc.code += rc.range & rc_bound; \
    dest = (dest << 1) + (rc_bound + 1); \
} while (0)
 
 
// NOTE: No macros are provided for bittree decoding. It seems to be simpler
// to just write them open in the code.
 
#endif