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// Copyright 2012 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Utilities for building and looking up Huffman trees.
//
// Author: Urvang Joshi (urvang@google.com)
#ifndef WEBP_UTILS_HUFFMAN_UTILS_H_
#define WEBP_UTILS_HUFFMAN_UTILS_H_
#include <assert.h>
#include "src/webp/format_constants.h"
#include "src/webp/types.h"
#ifdef __cplusplus
extern "C" {
#endif
#define HUFFMAN_TABLE_BITS 8
#define HUFFMAN_TABLE_MASK ((1 << HUFFMAN_TABLE_BITS) - 1)
#define LENGTHS_TABLE_BITS 7
#define LENGTHS_TABLE_MASK ((1 << LENGTHS_TABLE_BITS) - 1)
// Huffman lookup table entry
typedef struct {
uint8_t bits; // number of bits used for this symbol
uint16_t value; // symbol value or table offset
} HuffmanCode;
// long version for holding 32b values
typedef struct {
int bits; // number of bits used for this symbol,
// or an impossible value if not a literal code.
uint32_t value; // 32b packed ARGB value if literal,
// or non-literal symbol otherwise
} HuffmanCode32;
// Contiguous memory segment of HuffmanCodes.
typedef struct HuffmanTablesSegment {
HuffmanCode* start;
// Pointer to where we are writing into the segment. Starts at 'start' and
// cannot go beyond 'start' + 'size'.
HuffmanCode* curr_table;
// Pointer to the next segment in the chain.
struct HuffmanTablesSegment* next;
int size;
} HuffmanTablesSegment;
// Chained memory segments of HuffmanCodes.
typedef struct HuffmanTables {
HuffmanTablesSegment root;
// Currently processed segment. At first, this is 'root'.
HuffmanTablesSegment* curr_segment;
} HuffmanTables;
// Allocates a HuffmanTables with 'size' contiguous HuffmanCodes. Returns 0 on
// memory allocation error, 1 otherwise.
WEBP_NODISCARD int VP8LHuffmanTablesAllocate(int size,
HuffmanTables* huffman_tables);
void VP8LHuffmanTablesDeallocate(HuffmanTables* const huffman_tables);
#define HUFFMAN_PACKED_BITS 6
#define HUFFMAN_PACKED_TABLE_SIZE (1u << HUFFMAN_PACKED_BITS)
// Huffman table group.
// Includes special handling for the following cases:
// - is_trivial_literal: one common literal base for RED/BLUE/ALPHA (not GREEN)
// - is_trivial_code: only 1 code (no bit is read from bitstream)
// - use_packed_table: few enough literal symbols, so all the bit codes
// can fit into a small look-up table packed_table[]
// The common literal base, if applicable, is stored in 'literal_arb'.
typedef struct HTreeGroup HTreeGroup;
struct HTreeGroup {
HuffmanCode* htrees[HUFFMAN_CODES_PER_META_CODE];
int is_trivial_literal; // True, if huffman trees for Red, Blue & Alpha
// Symbols are trivial (have a single code).
uint32_t literal_arb; // If is_trivial_literal is true, this is the
// ARGB value of the pixel, with Green channel
// being set to zero.
int is_trivial_code; // true if is_trivial_literal with only one code
int use_packed_table; // use packed table below for short literal code
// table mapping input bits to a packed values, or escape case to literal code
HuffmanCode32 packed_table[HUFFMAN_PACKED_TABLE_SIZE];
};
// Creates the instance of HTreeGroup with specified number of tree-groups.
WEBP_NODISCARD HTreeGroup* VP8LHtreeGroupsNew(int num_htree_groups);
// Releases the memory allocated for HTreeGroup.
void VP8LHtreeGroupsFree(HTreeGroup* const htree_groups);
// Builds Huffman lookup table assuming code lengths are in symbol order.
// The 'code_lengths' is pre-allocated temporary memory buffer used for creating
// the huffman table.
// Returns built table size or 0 in case of error (invalid tree or
// memory error).
WEBP_NODISCARD int VP8LBuildHuffmanTable(HuffmanTables* const root_table,
int root_bits,
const int code_lengths[],
int code_lengths_size);
#ifdef __cplusplus
} // extern "C"
#endif
#endif // WEBP_UTILS_HUFFMAN_UTILS_H_
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