| // 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 |