179 lines
4.7 KiB
C
179 lines
4.7 KiB
C
///////////////////////////////////////////////////////////////////////////////
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//
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/// \file range_decoder.h
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/// \brief Range Decoder
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///
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// Authors: Igor Pavlov
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// Lasse Collin
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//
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// This file has been put into the public domain.
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// You can do whatever you want with this file.
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//
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///////////////////////////////////////////////////////////////////////////////
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#ifndef LZMA_RANGE_DECODER_H
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#define LZMA_RANGE_DECODER_H
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#include "range_common.h"
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typedef struct {
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uint32_t range;
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uint32_t code;
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uint32_t init_bytes_left;
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} lzma_range_decoder;
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/// Reads the first five bytes to initialize the range decoder.
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static inline bool
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rc_read_init(lzma_range_decoder *rc, const uint8_t *restrict in,
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size_t *restrict in_pos, size_t in_size)
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{
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while (rc->init_bytes_left > 0) {
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if (*in_pos == in_size)
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return false;
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rc->code = (rc->code << 8) | in[*in_pos];
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++*in_pos;
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--rc->init_bytes_left;
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}
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return true;
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}
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/// Makes local copies of range decoder and *in_pos variables. Doing this
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/// improves speed significantly. The range decoder macros expect also
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/// variables `in' and `in_size' to be defined.
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#define rc_to_local(range_decoder, in_pos) \
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lzma_range_decoder rc = range_decoder; \
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size_t rc_in_pos = (in_pos); \
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uint32_t rc_bound
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/// Stores the local copes back to the range decoder structure.
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#define rc_from_local(range_decoder, in_pos) \
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do { \
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range_decoder = rc; \
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in_pos = rc_in_pos; \
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} while (0)
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/// Resets the range decoder structure.
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#define rc_reset(range_decoder) \
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do { \
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(range_decoder).range = UINT32_MAX; \
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(range_decoder).code = 0; \
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(range_decoder).init_bytes_left = 5; \
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} while (0)
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/// When decoding has been properly finished, rc.code is always zero unless
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/// the input stream is corrupt. So checking this can catch some corrupt
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/// files especially if they don't have any other integrity check.
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#define rc_is_finished(range_decoder) \
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((range_decoder).code == 0)
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/// Read the next input byte if needed. If more input is needed but there is
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/// no more input available, "goto out" is used to jump out of the main
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/// decoder loop.
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#define rc_normalize(seq) \
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do { \
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if (rc.range < RC_TOP_VALUE) { \
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if (unlikely(rc_in_pos == in_size)) { \
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coder->sequence = seq; \
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goto out; \
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} \
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rc.range <<= RC_SHIFT_BITS; \
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rc.code = (rc.code << RC_SHIFT_BITS) | in[rc_in_pos++]; \
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} \
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} while (0)
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/// Start decoding a bit. This must be used together with rc_update_0()
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/// and rc_update_1():
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///
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/// rc_if_0(prob, seq) {
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/// rc_update_0(prob);
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/// // Do something
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/// } else {
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/// rc_update_1(prob);
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/// // Do something else
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/// }
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///
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#define rc_if_0(prob, seq) \
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rc_normalize(seq); \
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rc_bound = (rc.range >> RC_BIT_MODEL_TOTAL_BITS) * (prob); \
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if (rc.code < rc_bound)
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/// Update the range decoder state and the used probability variable to
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/// match a decoded bit of 0.
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#define rc_update_0(prob) \
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do { \
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rc.range = rc_bound; \
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prob += (RC_BIT_MODEL_TOTAL - (prob)) >> RC_MOVE_BITS; \
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} while (0)
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/// Update the range decoder state and the used probability variable to
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/// match a decoded bit of 1.
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#define rc_update_1(prob) \
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do { \
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rc.range -= rc_bound; \
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rc.code -= rc_bound; \
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prob -= (prob) >> RC_MOVE_BITS; \
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} while (0)
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/// Decodes one bit and runs action0 or action1 depending on the decoded bit.
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/// This macro is used as the last step in bittree reverse decoders since
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/// those don't use "symbol" for anything else than indexing the probability
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/// arrays.
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#define rc_bit_last(prob, action0, action1, seq) \
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do { \
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rc_if_0(prob, seq) { \
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rc_update_0(prob); \
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action0; \
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} else { \
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rc_update_1(prob); \
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action1; \
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} \
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} while (0)
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/// Decodes one bit, updates "symbol", and runs action0 or action1 depending
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/// on the decoded bit.
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#define rc_bit(prob, action0, action1, seq) \
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rc_bit_last(prob, \
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symbol <<= 1; action0, \
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symbol = (symbol << 1) + 1; action1, \
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seq);
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/// Like rc_bit() but add "case seq:" as a prefix. This makes the unrolled
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/// loops more readable because the code isn't littered with "case"
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/// statements. On the other hand this also makes it less readable, since
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/// spotting the places where the decoder loop may be restarted is less
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/// obvious.
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#define rc_bit_case(prob, action0, action1, seq) \
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case seq: rc_bit(prob, action0, action1, seq)
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/// Decode a bit without using a probability.
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#define rc_direct(dest, seq) \
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do { \
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rc_normalize(seq); \
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rc.range >>= 1; \
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rc.code -= rc.range; \
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rc_bound = UINT32_C(0) - (rc.code >> 31); \
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rc.code += rc.range & rc_bound; \
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dest = (dest << 1) + (rc_bound + 1); \
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} while (0)
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// NOTE: No macros are provided for bittree decoding. It seems to be simpler
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// to just write them open in the code.
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#endif
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