--- /dev/null
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file range_decoder.h
+/// \brief Range Decoder
+///
+// 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;
+
+
+/// Reads the first five bytes to initialize the 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;
+}
+
+
+/// Makes local copies of range decoder and *in_pos variables. Doing this
+/// improves speed significantly. The range decoder macros expect also
+/// variables `in' and `in_size' to be defined.
+#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
+
+
+/// Stores the local copes back to the range decoder structure.
+#define rc_from_local(range_decoder, in_pos) \
+do { \
+ range_decoder = rc; \
+ in_pos = rc_in_pos; \
+} while (0)
+
+
+/// Resets the range decoder structure.
+#define rc_reset(range_decoder) \
+do { \
+ (range_decoder).range = UINT32_MAX; \
+ (range_decoder).code = 0; \
+ (range_decoder).init_bytes_left = 5; \
+} while (0)
+
+
+/// When decoding has been properly finished, rc.code is always zero unless
+/// the input stream is corrupt. So checking this can catch some corrupt
+/// files especially if they don't have any other integrity check.
+#define rc_is_finished(range_decoder) \
+ ((range_decoder).code == 0)
+
+
+/// Read the next input byte if needed. If more input is needed but there is
+/// no more input available, "goto out" is used to jump out of the main
+/// decoder loop.
+#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)
+
+
+/// Start decoding a bit. This must be used together with rc_update_0()
+/// and rc_update_1():
+///
+/// rc_if_0(prob, seq) {
+/// rc_update_0(prob);
+/// // Do something
+/// } else {
+/// rc_update_1(prob);
+/// // Do something else
+/// }
+///
+#define rc_if_0(prob, seq) \
+ rc_normalize(seq); \
+ rc_bound = (rc.range >> RC_BIT_MODEL_TOTAL_BITS) * (prob); \
+ if (rc.code < rc_bound)
+
+
+/// Update the range decoder state and the used probability variable to
+/// match a decoded bit of 0.
+#define rc_update_0(prob) \
+do { \
+ rc.range = rc_bound; \
+ prob += (RC_BIT_MODEL_TOTAL - (prob)) >> RC_MOVE_BITS; \
+} while (0)
+
+
+/// Update the range decoder state and the used probability variable to
+/// match a decoded bit of 1.
+#define rc_update_1(prob) \
+do { \
+ rc.range -= rc_bound; \
+ rc.code -= rc_bound; \
+ prob -= (prob) >> RC_MOVE_BITS; \
+} while (0)
+
+
+/// Decodes one bit and runs action0 or action1 depending on the decoded bit.
+/// This macro is used as the last step in bittree reverse decoders since
+/// those don't use "symbol" for anything else than indexing the probability
+/// arrays.
+#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)
+
+
+/// Decodes one bit, updates "symbol", and runs action0 or action1 depending
+/// on the decoded bit.
+#define rc_bit(prob, action0, action1, seq) \
+ rc_bit_last(prob, \
+ symbol <<= 1; action0, \
+ symbol = (symbol << 1) + 1; action1, \
+ seq);
+
+
+/// Like rc_bit() but add "case seq:" as a prefix. This makes the unrolled
+/// loops more readable because the code isn't littered with "case"
+/// statements. On the other hand this also makes it less readable, since
+/// spotting the places where the decoder loop may be restarted is less
+/// obvious.
+#define rc_bit_case(prob, action0, action1, seq) \
+ case seq: rc_bit(prob, action0, action1, seq)
+
+
+/// Decode a bit without using a probability.
+#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
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