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// Copyright 2013 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Functions for encoding of integers into prefix codes the amount of extra
// bits, and the actual values of the extra bits.
#include "./prefix.h"
#include "./fast_log.h"
namespace brotli {
// Represents the range of values belonging to a prefix code:
// [offset, offset + 2^nbits)
struct PrefixCodeRange {
int offset;
int 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}
};
static const PrefixCodeRange kInsertLengthPrefixCode[kNumInsertLenPrefixes] = {
{ 0, 0}, { 1, 0}, { 2, 0}, { 3, 0},
{ 4, 0}, { 5, 0}, { 6, 1}, { 8, 1},
{ 10, 2}, { 14, 2}, { 18, 3}, { 26, 3},
{ 34, 4}, { 50, 4}, { 66, 5}, { 98, 5},
{ 130, 6}, { 194, 7}, { 322, 8}, { 578, 9},
{1090, 10}, {2114, 12}, {6210, 14}, {22594, 24},
};
static const PrefixCodeRange kCopyLengthPrefixCode[kNumCopyLenPrefixes] = {
{ 2, 0}, { 3, 0}, { 4, 0}, { 5, 0},
{ 6, 0}, { 7, 0}, { 8, 0}, { 9, 0},
{ 10, 1}, { 12, 1}, { 14, 2}, { 18, 2},
{ 22, 3}, { 30, 3}, { 38, 4}, { 54, 4},
{ 70, 5}, { 102, 5}, { 134, 6}, { 198, 7},
{326, 8}, { 582, 9}, {1094, 10}, {2118, 24},
};
static const int kInsertAndCopyRangeLut[9] = {
0, 1, 4, 2, 3, 6, 5, 7, 8,
};
static const int kInsertRangeLut[9] = {
0, 0, 1, 1, 0, 2, 1, 2, 2,
};
static const int kCopyRangeLut[9] = {
0, 1, 0, 1, 2, 0, 2, 1, 2,
};
int InsertLengthPrefix(int length) {
for (int i = 0; i < kNumInsertLenPrefixes; ++i) {
const PrefixCodeRange& range = kInsertLengthPrefixCode[i];
if (length >= range.offset && length < range.offset + (1 << range.nbits)) {
return i;
}
}
return -1;
}
int CopyLengthPrefix(int length) {
for (int i = 0; i < kNumCopyLenPrefixes; ++i) {
const PrefixCodeRange& range = kCopyLengthPrefixCode[i];
if (length >= range.offset && length < range.offset + (1 << range.nbits)) {
return i;
}
}
return -1;
}
int CommandPrefix(int insert_length, int copy_length) {
if (copy_length == 0) {
copy_length = 3;
}
int insert_prefix = InsertLengthPrefix(insert_length);
int copy_prefix = CopyLengthPrefix(copy_length);
int range_idx = 3 * (insert_prefix >> 3) + (copy_prefix >> 3);
return ((kInsertAndCopyRangeLut[range_idx] << 6) +
((insert_prefix & 7) << 3) + (copy_prefix & 7));
}
int InsertLengthExtraBits(int code) {
int insert_code = (kInsertRangeLut[code >> 6] << 3) + ((code >> 3) & 7);
return kInsertLengthPrefixCode[insert_code].nbits;
}
int InsertLengthOffset(int code) {
int insert_code = (kInsertRangeLut[code >> 6] << 3) + ((code >> 3) & 7);
return kInsertLengthPrefixCode[insert_code].offset;
}
int CopyLengthExtraBits(int code) {
int copy_code = (kCopyRangeLut[code >> 6] << 3) + (code & 7);
return kCopyLengthPrefixCode[copy_code].nbits;
}
int CopyLengthOffset(int code) {
int copy_code = (kCopyRangeLut[code >> 6] << 3) + (code & 7);
return kCopyLengthPrefixCode[copy_code].offset;
}
void PrefixEncodeCopyDistance(int distance_code,
int num_direct_codes,
int postfix_bits,
uint16_t* code,
int* nbits,
uint32_t* extra_bits) {
distance_code -= 1;
if (distance_code < kNumDistanceShortCodes + num_direct_codes) {
*code = distance_code;
*nbits = 0;
*extra_bits = 0;
return;
}
distance_code -= kNumDistanceShortCodes + num_direct_codes;
distance_code += (1 << (postfix_bits + 2));
int bucket = Log2Floor(distance_code) - 1;
int postfix_mask = (1 << postfix_bits) - 1;
int postfix = distance_code & postfix_mask;
int prefix = (distance_code >> bucket) & 1;
int offset = (2 + prefix) << bucket;
*nbits = bucket - postfix_bits;
*code = kNumDistanceShortCodes + num_direct_codes +
((2 * (*nbits - 1) + prefix) << postfix_bits) + postfix;
*extra_bits = (distance_code - offset) >> postfix_bits;
}
int BlockLengthPrefix(int length) {
for (int i = 0; i < kNumBlockLenPrefixes; ++i) {
const PrefixCodeRange& range = kBlockLengthPrefixCode[i];
if (length >= range.offset && length < range.offset + (1 << range.nbits)) {
return i;
}
}
return -1;
}
int BlockLengthExtraBits(int length_code) {
return kBlockLengthPrefixCode[length_code].nbits;
}
int BlockLengthOffset(int length_code) {
return kBlockLengthPrefixCode[length_code].offset;
}
} // namespace brotli
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