--- /dev/null
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file lzma_common.h
+/// \brief Private definitions common to LZMA encoder and 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_LZMA_COMMON_H
+#define LZMA_LZMA_COMMON_H
+
+#include "common.h"
+#include "range_common.h"
+
+
+///////////////////
+// Miscellaneous //
+///////////////////
+
+/// Maximum number of position states. A position state is the lowest pos bits
+/// number of bits of the current uncompressed offset. In some places there
+/// are different sets of probabilities for different pos states.
+#define POS_STATES_MAX (1 << LZMA_PB_MAX)
+
+
+/// Validates lc, lp, and pb.
+static inline bool
+is_lclppb_valid(const lzma_options_lzma *options)
+{
+ return options->lc <= LZMA_LCLP_MAX && options->lp <= LZMA_LCLP_MAX
+ && options->lc + options->lp <= LZMA_LCLP_MAX
+ && options->pb <= LZMA_PB_MAX;
+}
+
+
+///////////
+// State //
+///////////
+
+/// This enum is used to track which events have occurred most recently and
+/// in which order. This information is used to predict the next event.
+///
+/// Events:
+/// - Literal: One 8-bit byte
+/// - Match: Repeat a chunk of data at some distance
+/// - Long repeat: Multi-byte match at a recently seen distance
+/// - Short repeat: One-byte repeat at a recently seen distance
+///
+/// The event names are in from STATE_oldest_older_previous. REP means
+/// either short or long repeated match, and NONLIT means any non-literal.
+typedef enum {
+ STATE_LIT_LIT,
+ STATE_MATCH_LIT_LIT,
+ STATE_REP_LIT_LIT,
+ STATE_SHORTREP_LIT_LIT,
+ STATE_MATCH_LIT,
+ STATE_REP_LIT,
+ STATE_SHORTREP_LIT,
+ STATE_LIT_MATCH,
+ STATE_LIT_LONGREP,
+ STATE_LIT_SHORTREP,
+ STATE_NONLIT_MATCH,
+ STATE_NONLIT_REP,
+} lzma_lzma_state;
+
+
+/// Total number of states
+#define STATES 12
+
+/// The lowest 7 states indicate that the previous state was a literal.
+#define LIT_STATES 7
+
+
+/// Indicate that the latest state was a literal.
+#define update_literal(state) \
+ state = ((state) <= STATE_SHORTREP_LIT_LIT \
+ ? STATE_LIT_LIT \
+ : ((state) <= STATE_LIT_SHORTREP \
+ ? (state) - 3 \
+ : (state) - 6))
+
+/// Indicate that the latest state was a match.
+#define update_match(state) \
+ state = ((state) < LIT_STATES ? STATE_LIT_MATCH : STATE_NONLIT_MATCH)
+
+/// Indicate that the latest state was a long repeated match.
+#define update_long_rep(state) \
+ state = ((state) < LIT_STATES ? STATE_LIT_LONGREP : STATE_NONLIT_REP)
+
+/// Indicate that the latest state was a short match.
+#define update_short_rep(state) \
+ state = ((state) < LIT_STATES ? STATE_LIT_SHORTREP : STATE_NONLIT_REP)
+
+/// Test if the previous state was a literal.
+#define is_literal_state(state) \
+ ((state) < LIT_STATES)
+
+
+/////////////
+// Literal //
+/////////////
+
+/// Each literal coder is divided in three sections:
+/// - 0x001-0x0FF: Without match byte
+/// - 0x101-0x1FF: With match byte; match bit is 0
+/// - 0x201-0x2FF: With match byte; match bit is 1
+///
+/// Match byte is used when the previous LZMA symbol was something else than
+/// a literal (that is, it was some kind of match).
+#define LITERAL_CODER_SIZE 0x300
+
+/// Maximum number of literal coders
+#define LITERAL_CODERS_MAX (1 << LZMA_LCLP_MAX)
+
+/// Locate the literal coder for the next literal byte. The choice depends on
+/// - the lowest literal_pos_bits bits of the position of the current
+/// byte; and
+/// - the highest literal_context_bits bits of the previous byte.
+#define literal_subcoder(probs, lc, lp_mask, pos, prev_byte) \
+ ((probs)[(((pos) & lp_mask) << lc) + ((prev_byte) >> (8 - lc))])
+
+
+static inline void
+literal_init(probability (*probs)[LITERAL_CODER_SIZE],
+ uint32_t lc, uint32_t lp)
+{
+ assert(lc + lp <= LZMA_LCLP_MAX);
+
+ const uint32_t coders = 1U << (lc + lp);
+
+ for (uint32_t i = 0; i < coders; ++i)
+ for (uint32_t j = 0; j < LITERAL_CODER_SIZE; ++j)
+ bit_reset(probs[i][j]);
+
+ return;
+}
+
+
+//////////////////
+// Match length //
+//////////////////
+
+// Minimum length of a match is two bytes.
+#define MATCH_LEN_MIN 2
+
+// Match length is encoded with 4, 5, or 10 bits.
+//
+// Length Bits
+// 2-9 4 = Choice=0 + 3 bits
+// 10-17 5 = Choice=1 + Choice2=0 + 3 bits
+// 18-273 10 = Choice=1 + Choice2=1 + 8 bits
+#define LEN_LOW_BITS 3
+#define LEN_LOW_SYMBOLS (1 << LEN_LOW_BITS)
+#define LEN_MID_BITS 3
+#define LEN_MID_SYMBOLS (1 << LEN_MID_BITS)
+#define LEN_HIGH_BITS 8
+#define LEN_HIGH_SYMBOLS (1 << LEN_HIGH_BITS)
+#define LEN_SYMBOLS (LEN_LOW_SYMBOLS + LEN_MID_SYMBOLS + LEN_HIGH_SYMBOLS)
+
+// Maximum length of a match is 273 which is a result of the encoding
+// described above.
+#define MATCH_LEN_MAX (MATCH_LEN_MIN + LEN_SYMBOLS - 1)
+
+
+////////////////////
+// Match distance //
+////////////////////
+
+// Different sets of probabilities are used for match distances that have very
+// short match length: Lengths of 2, 3, and 4 bytes have a separate set of
+// probabilities for each length. The matches with longer length use a shared
+// set of probabilities.
+#define DIST_STATES 4
+
+// Macro to get the index of the appropriate probability array.
+#define get_dist_state(len) \
+ ((len) < DIST_STATES + MATCH_LEN_MIN \
+ ? (len) - MATCH_LEN_MIN \
+ : DIST_STATES - 1)
+
+// The highest two bits of a match distance (distance slot) are encoded
+// using six bits. See fastpos.h for more explanation.
+#define DIST_SLOT_BITS 6
+#define DIST_SLOTS (1 << DIST_SLOT_BITS)
+
+// Match distances up to 127 are fully encoded using probabilities. Since
+// the highest two bits (distance slot) are always encoded using six bits,
+// the distances 0-3 don't need any additional bits to encode, since the
+// distance slot itself is the same as the actual distance. DIST_MODEL_START
+// indicates the first distance slot where at least one additional bit is
+// needed.
+#define DIST_MODEL_START 4
+
+// Match distances greater than 127 are encoded in three pieces:
+// - distance slot: the highest two bits
+// - direct bits: 2-26 bits below the highest two bits
+// - alignment bits: four lowest bits
+//
+// Direct bits don't use any probabilities.
+//
+// The distance slot value of 14 is for distances 128-191 (see the table in
+// fastpos.h to understand why).
+#define DIST_MODEL_END 14
+
+// Distance slots that indicate a distance <= 127.
+#define FULL_DISTANCES_BITS (DIST_MODEL_END / 2)
+#define FULL_DISTANCES (1 << FULL_DISTANCES_BITS)
+
+// For match distances greater than 127, only the highest two bits and the
+// lowest four bits (alignment) is encoded using probabilities.
+#define ALIGN_BITS 4
+#define ALIGN_SIZE (1 << ALIGN_BITS)
+#define ALIGN_MASK (ALIGN_SIZE - 1)
+
+// LZMA remembers the four most recent match distances. Reusing these distances
+// tends to take less space than re-encoding the actual distance value.
+#define REPS 4
+
+#endif
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