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/*++
Copyright (c) Alex Ionescu. All rights reserved.
Module Name:
lzmadec.h
Abstract:
This header file contains C-style definitions, constants, and enumerations
that map back to the LZMA Standard, specifically the probability model that
is used for encoding probabilities.
Author:
Alex Ionescu (@aionescu) 15-Apr-2020 - Initial version
Environment:
Windows & Linux, user mode and kernel mode.
--*/
#pragma once
//
// Literals can be 0-255 and are encoded in 3 different types of slots based on
// the previous literal decoded and the "match byte" used.
//
#define LZMA_LITERALS 256
#define LZMA_LC_TYPES 3
#define LZMA_LC_MODEL_SIZE (LZMA_LC_TYPES * LZMA_LITERALS)
//
// These are the hardcoded LZMA properties we support for position and coders
//
#define LZMA_LC 3
#define LZMA_PB 2
#define LZMA_LP 0
#define LZMA_LITERAL_CODERS (1 << LZMA_LC)
#define LZMA_POSITION_COUNT (1 << LZMA_PB)
//
// Lengths are described in three different ways using "low", "mid", and "high"
// bit trees. The first two trees encode 3 bits, the last encodes 8. We never
// encode a length less than 2 bytes, since that's wasteful.
//
#define LZMA_MAX_LOW_LENGTH (1 << 3)
#define LZMA_MAX_MID_LENGTH (1 << 3)
#define LZMA_MAX_HIGH_LENGTH (1 << 8)
#define LZMA_MIN_LENGTH 2
//
// Distances can be encoded in different ways, based on the distance slot.
// Lengths of 2, 3, 4 bytes are directly encoded with their own slot. Lengths
// over 5 share a slot, which is then further subdivded into 3 different ways
// of encoding them, which are described in the source.
//
#define LZMA_DISTANCE_SLOTS 64
#define LZMA_FIRST_CONTEXT_DISTANCE_SLOT 4
#define LZMA_FIRST_FIXED_DISTANCE_SLOT 14
#define LZMA_DISTANCE_ALIGN_BITS 4
#define LZMA_DISTANCE_ALIGN_SLOTS (1 << LZMA_DISTANCE_ALIGN_BITS)
//
// Total number of probabilities that we need to store
//
#define LZMA_BIT_MODEL_SLOTS (1174 + \
(LZMA_LITERAL_CODERS * \
LZMA_LC_MODEL_SIZE))
//
// The LZMA probability bit model is typically based on the last LZMA sequences
// that were decoded. There are 11 such possibilities that are tracked.
//
typedef enum _LZMA_SEQUENCE_STATE
{
//
// State where we last saw three literals
//
LzmaLitLitLitState,
//
// States where we last saw two literals preceeded by a non-literal
//
LzmaMatchLitLitState,
LzmaRepLitLitState,
LzmaLitShortrepLitLitState,
//
// States where we last saw one literal preceeded by a non-literal
//
LzmaMatchLitState,
LzmaRepLitState,
LzmaLitShortrepLitState,
//
// Separator between states where we last saw at least one literal
//
LzmaMaxLitState,
//
// States where we last saw a non-literal preceeded by a literal
//
LzmaLitMatchState = 7,
LzmaLitRepState,
LzmaLitShortrepState,
//
// States where we last saw two non-literals
//
LzmaNonlitMatchState,
LzmaNonlitRepState,
//
// Separator for number of total states
//
LzmaMaxState
} LZMA_SEQUENCE_STATE, * PLZMA_SEQUENCE_STATE;
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