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/* Copyright 2013 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
// Functions for encoding of integers into prefix codes the amount of extra
// bits, and the actual values of the extra bits.
#ifndef BROTLI_ENC_PREFIX_H_
#define BROTLI_ENC_PREFIX_H_
#include "./fast_log.h"
#include "./types.h"
namespace brotli {
static const uint32_t kNumInsertLenPrefixes = 24;
static const uint32_t kNumCopyLenPrefixes = 24;
static const uint32_t kNumCommandPrefixes = 704;
static const uint32_t kNumBlockLenPrefixes = 26;
static const uint32_t kNumDistanceShortCodes = 16;
static const uint32_t kNumDistancePrefixes = 520;
// Represents the range of values belonging to a prefix code:
// [offset, offset + 2^nbits)
struct PrefixCodeRange {
uint32_t offset;
uint32_t nbits;
};
static const PrefixCodeRange kBlockLengthPrefixCode[kNumBlockLenPrefixes] = {
{ 1, 2}, { 5, 2}, { 9, 2}, { 13, 2},
{ 17, 3}, { 25, 3}, { 33, 3}, { 41, 3},
{ 49, 4}, { 65, 4}, { 81, 4}, { 97, 4},
{ 113, 5}, { 145, 5}, { 177, 5}, { 209, 5},
{ 241, 6}, { 305, 6}, { 369, 7}, { 497, 8},
{ 753, 9}, { 1265, 10}, {2289, 11}, {4337, 12},
{8433, 13}, {16625, 24}
};
inline void GetBlockLengthPrefixCode(uint32_t len, uint32_t* code,
uint32_t* n_extra, uint32_t* extra) {
*code = 0;
while (*code < 25 && len >= kBlockLengthPrefixCode[*code + 1].offset) {
++(*code);
}
*n_extra = kBlockLengthPrefixCode[*code].nbits;
*extra = len - kBlockLengthPrefixCode[*code].offset;
}
inline void PrefixEncodeCopyDistance(size_t distance_code,
size_t num_direct_codes,
size_t postfix_bits,
uint16_t* code,
uint32_t* extra_bits) {
if (distance_code < kNumDistanceShortCodes + num_direct_codes) {
*code = static_cast<uint16_t>(distance_code);
*extra_bits = 0;
return;
}
distance_code -= kNumDistanceShortCodes + num_direct_codes; /* >= 0 */
distance_code += (1 << (postfix_bits + 2)); /* > 0 */
size_t bucket = Log2FloorNonZero(distance_code) - 1;
size_t postfix_mask = (1 << postfix_bits) - 1;
size_t postfix = distance_code & postfix_mask;
size_t prefix = (distance_code >> bucket) & 1;
size_t offset = (2 + prefix) << bucket;
size_t nbits = bucket - postfix_bits;
*code = static_cast<uint16_t>(
(kNumDistanceShortCodes + num_direct_codes +
((2 * (nbits - 1) + prefix) << postfix_bits) + postfix));
*extra_bits = static_cast<uint32_t>(
(nbits << 24) | ((distance_code - offset) >> postfix_bits));
}
} // namespace brotli
#endif // BROTLI_ENC_PREFIX_H_
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