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-/* Copyright 2016 Google Inc. All Rights Reserved.
-
- Distributed under MIT license.
- See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
-*/
-
-/**
- * @file
- * Common constants used in decoder and encoder API.
- */
-
-#ifndef BROTLI_COMMON_CONSTANTS_H_
-#define BROTLI_COMMON_CONSTANTS_H_
-
-#include "./platform.h"
-#include <brotli/port.h>
-#include <brotli/types.h>
-
-/* Specification: 7.3. Encoding of the context map */
-#define BROTLI_CONTEXT_MAP_MAX_RLE 16
-
-/* Specification: 2. Compressed representation overview */
-#define BROTLI_MAX_NUMBER_OF_BLOCK_TYPES 256
-
-/* Specification: 3.3. Alphabet sizes: insert-and-copy length */
-#define BROTLI_NUM_LITERAL_SYMBOLS 256
-#define BROTLI_NUM_COMMAND_SYMBOLS 704
-#define BROTLI_NUM_BLOCK_LEN_SYMBOLS 26
-#define BROTLI_MAX_CONTEXT_MAP_SYMBOLS (BROTLI_MAX_NUMBER_OF_BLOCK_TYPES + \
- BROTLI_CONTEXT_MAP_MAX_RLE)
-#define BROTLI_MAX_BLOCK_TYPE_SYMBOLS (BROTLI_MAX_NUMBER_OF_BLOCK_TYPES + 2)
-
-/* Specification: 3.5. Complex prefix codes */
-#define BROTLI_REPEAT_PREVIOUS_CODE_LENGTH 16
-#define BROTLI_REPEAT_ZERO_CODE_LENGTH 17
-#define BROTLI_CODE_LENGTH_CODES (BROTLI_REPEAT_ZERO_CODE_LENGTH + 1)
-/* "code length of 8 is repeated" */
-#define BROTLI_INITIAL_REPEATED_CODE_LENGTH 8
-
-/* "Large Window Brotli" */
-
-/**
- * The theoretical maximum number of distance bits specified for large window
- * brotli, for 64-bit encoders and decoders. Even when in practice 32-bit
- * encoders and decoders only support up to 30 max distance bits, the value is
- * set to 62 because it affects the large window brotli file format.
- * Specifically, it affects the encoding of simple huffman tree for distances,
- * see Specification RFC 7932 chapter 3.4.
- */
-#define BROTLI_LARGE_MAX_DISTANCE_BITS 62U
-#define BROTLI_LARGE_MIN_WBITS 10
-/**
- * The maximum supported large brotli window bits by the encoder and decoder.
- * Large window brotli allows up to 62 bits, however the current encoder and
- * decoder, designed for 32-bit integers, only support up to 30 bits maximum.
- */
-#define BROTLI_LARGE_MAX_WBITS 30
-
-/* Specification: 4. Encoding of distances */
-#define BROTLI_NUM_DISTANCE_SHORT_CODES 16
-/**
- * Maximal number of "postfix" bits.
- *
- * Number of "postfix" bits is stored as 2 bits in meta-block header.
- */
-#define BROTLI_MAX_NPOSTFIX 3
-#define BROTLI_MAX_NDIRECT 120
-#define BROTLI_MAX_DISTANCE_BITS 24U
-#define BROTLI_DISTANCE_ALPHABET_SIZE(NPOSTFIX, NDIRECT, MAXNBITS) ( \
- BROTLI_NUM_DISTANCE_SHORT_CODES + (NDIRECT) + \
- ((MAXNBITS) << ((NPOSTFIX) + 1)))
-/* BROTLI_NUM_DISTANCE_SYMBOLS == 1128 */
-#define BROTLI_NUM_DISTANCE_SYMBOLS \
- BROTLI_DISTANCE_ALPHABET_SIZE( \
- BROTLI_MAX_NDIRECT, BROTLI_MAX_NPOSTFIX, BROTLI_LARGE_MAX_DISTANCE_BITS)
-
-/* ((1 << 26) - 4) is the maximal distance that can be expressed in RFC 7932
- brotli stream using NPOSTFIX = 0 and NDIRECT = 0. With other NPOSTFIX and
- NDIRECT values distances up to ((1 << 29) + 88) could be expressed. */
-#define BROTLI_MAX_DISTANCE 0x3FFFFFC
-
-/* ((1 << 31) - 4) is the safe distance limit. Using this number as a limit
- allows safe distance calculation without overflows, given the distance
- alphabet size is limited to corresponding size
- (see kLargeWindowDistanceCodeLimits). */
-#define BROTLI_MAX_ALLOWED_DISTANCE 0x7FFFFFFC
-
-
-/* Specification: 4. Encoding of Literal Insertion Lengths and Copy Lengths */
-#define BROTLI_NUM_INS_COPY_CODES 24
-
-/* 7.1. Context modes and context ID lookup for literals */
-/* "context IDs for literals are in the range of 0..63" */
-#define BROTLI_LITERAL_CONTEXT_BITS 6
-
-/* 7.2. Context ID for distances */
-#define BROTLI_DISTANCE_CONTEXT_BITS 2
-
-/* 9.1. Format of the Stream Header */
-/* Number of slack bytes for window size. Don't confuse
- with BROTLI_NUM_DISTANCE_SHORT_CODES. */
-#define BROTLI_WINDOW_GAP 16
-#define BROTLI_MAX_BACKWARD_LIMIT(W) (((size_t)1 << (W)) - BROTLI_WINDOW_GAP)
-
-typedef struct BrotliDistanceCodeLimit {
- uint32_t max_alphabet_size;
- uint32_t max_distance;
-} BrotliDistanceCodeLimit;
-
-/* This function calculates maximal size of distance alphabet, such that the
- distances greater than the given values can not be represented.
-
- This limits are designed to support fast and safe 32-bit decoders.
- "32-bit" means that signed integer values up to ((1 << 31) - 1) could be
- safely expressed.
-
- Brotli distance alphabet symbols do not represent consecutive distance
- ranges. Each distance alphabet symbol (excluding direct distances and short
- codes), represent interleaved (for NPOSTFIX > 0) range of distances.
- A "group" of consecutive (1 << NPOSTFIX) symbols represent non-interleaved
- range. Two consecutive groups require the same amount of "extra bits".
-
- It is important that distance alphabet represents complete "groups".
- To avoid complex logic on encoder side about interleaved ranges
- it was decided to restrict both sides to complete distance code "groups".
- */
-BROTLI_UNUSED_FUNCTION BrotliDistanceCodeLimit BrotliCalculateDistanceCodeLimit(
- uint32_t max_distance, uint32_t npostfix, uint32_t ndirect) {
- BrotliDistanceCodeLimit result;
- /* Marking this function as unused, because not all files
- including "constants.h" use it -> compiler warns about that. */
- BROTLI_UNUSED(&BrotliCalculateDistanceCodeLimit);
- if (max_distance <= ndirect) {
- /* This case never happens / exists only for the sake of completeness. */
- result.max_alphabet_size = max_distance + BROTLI_NUM_DISTANCE_SHORT_CODES;
- result.max_distance = max_distance;
- return result;
- } else {
- /* The first prohibited value. */
- uint32_t forbidden_distance = max_distance + 1;
- /* Subtract "directly" encoded region. */
- uint32_t offset = forbidden_distance - ndirect - 1;
- uint32_t ndistbits = 0;
- uint32_t tmp;
- uint32_t half;
- uint32_t group;
- /* Postfix for the last dcode in the group. */
- uint32_t postfix = (1u << npostfix) - 1;
- uint32_t extra;
- uint32_t start;
- /* Remove postfix and "head-start". */
- offset = (offset >> npostfix) + 4;
- /* Calculate the number of distance bits. */
- tmp = offset / 2;
- /* Poor-man's log2floor, to avoid extra dependencies. */
- while (tmp != 0) {ndistbits++; tmp = tmp >> 1;}
- /* One bit is covered with subrange addressing ("half"). */
- ndistbits--;
- /* Find subrange. */
- half = (offset >> ndistbits) & 1;
- /* Calculate the "group" part of dcode. */
- group = ((ndistbits - 1) << 1) | half;
- /* Calculated "group" covers the prohibited distance value. */
- if (group == 0) {
- /* This case is added for correctness; does not occur for limit > 128. */
- result.max_alphabet_size = ndirect + BROTLI_NUM_DISTANCE_SHORT_CODES;
- result.max_distance = ndirect;
- return result;
- }
- /* Decrement "group", so it is the last permitted "group". */
- group--;
- /* After group was decremented, ndistbits and half must be recalculated. */
- ndistbits = (group >> 1) + 1;
- /* The last available distance in the subrange has all extra bits set. */
- extra = (1u << ndistbits) - 1;
- /* Calculate region start. NB: ndistbits >= 1. */
- start = (1u << (ndistbits + 1)) - 4;
- /* Move to subregion. */
- start += (group & 1) << ndistbits;
- /* Calculate the alphabet size. */
- result.max_alphabet_size = ((group << npostfix) | postfix) + ndirect +
- BROTLI_NUM_DISTANCE_SHORT_CODES + 1;
- /* Calculate the maximal distance representable by alphabet. */
- result.max_distance = ((start + extra) << npostfix) + postfix + ndirect + 1;
- return result;
- }
-}
-
-/* Represents the range of values belonging to a prefix code:
- [offset, offset + 2^nbits) */
-typedef struct {
- uint16_t offset;
- uint8_t nbits;
-} BrotliPrefixCodeRange;
-
-/* "Soft-private", it is exported, but not "advertised" as API. */
-BROTLI_COMMON_API extern const BrotliPrefixCodeRange
- _kBrotliPrefixCodeRanges[BROTLI_NUM_BLOCK_LEN_SYMBOLS];
-
-#endif /* BROTLI_COMMON_CONSTANTS_H_ */