Zoltan Szabadka | c66e4e3 | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 1 | // Copyright 2013 Google Inc. All Rights Reserved. |
| 2 | // |
| 3 | // Licensed under the Apache License, Version 2.0 (the "License"); |
| 4 | // you may not use this file except in compliance with the License. |
| 5 | // You may obtain a copy of the License at |
| 6 | // |
| 7 | // http://www.apache.org/licenses/LICENSE-2.0 |
| 8 | // |
| 9 | // Unless required by applicable law or agreed to in writing, software |
| 10 | // distributed under the License is distributed on an "AS IS" BASIS, |
| 11 | // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 12 | // See the License for the specific language governing permissions and |
| 13 | // limitations under the License. |
| 14 | // |
| 15 | // Functions for encoding of integers into prefix codes the amount of extra |
| 16 | // bits, and the actual values of the extra bits. |
| 17 | |
| 18 | #include "./prefix.h" |
| 19 | |
| 20 | #include "./fast_log.h" |
| 21 | |
| 22 | namespace brotli { |
| 23 | |
| 24 | // Represents the range of values belonging to a prefix code: |
| 25 | // [offset, offset + 2^nbits) |
| 26 | struct PrefixCodeRange { |
| 27 | int offset; |
| 28 | int nbits; |
| 29 | }; |
| 30 | |
| 31 | static const PrefixCodeRange kBlockLengthPrefixCode[kNumBlockLenPrefixes] = { |
| 32 | { 1, 2}, { 5, 2}, { 9, 2}, { 13, 2}, |
| 33 | { 17, 3}, { 25, 3}, { 33, 3}, { 41, 3}, |
| 34 | { 49, 4}, { 65, 4}, { 81, 4}, { 97, 4}, |
| 35 | { 113, 5}, { 145, 5}, { 177, 5}, { 209, 5}, |
| 36 | { 241, 6}, { 305, 6}, { 369, 7}, { 497, 8}, |
| 37 | { 753, 9}, { 1265, 10}, {2289, 11}, {4337, 12}, |
| 38 | {8433, 13}, {16625, 24} |
| 39 | }; |
| 40 | |
| 41 | static const PrefixCodeRange kInsertLengthPrefixCode[kNumInsertLenPrefixes] = { |
| 42 | { 0, 0}, { 1, 0}, { 2, 0}, { 3, 0}, |
| 43 | { 4, 0}, { 5, 0}, { 6, 1}, { 8, 1}, |
| 44 | { 10, 2}, { 14, 2}, { 18, 3}, { 26, 3}, |
| 45 | { 34, 4}, { 50, 4}, { 66, 5}, { 98, 5}, |
| 46 | { 130, 6}, { 194, 7}, { 322, 8}, { 578, 9}, |
| 47 | {1090, 10}, {2114, 12}, {6210, 14}, {22594, 24}, |
| 48 | }; |
| 49 | |
| 50 | static const PrefixCodeRange kCopyLengthPrefixCode[kNumCopyLenPrefixes] = { |
| 51 | { 2, 0}, { 3, 0}, { 4, 0}, { 5, 0}, |
| 52 | { 6, 0}, { 7, 0}, { 8, 0}, { 9, 0}, |
| 53 | { 10, 1}, { 12, 1}, { 14, 2}, { 18, 2}, |
| 54 | { 22, 3}, { 30, 3}, { 38, 4}, { 54, 4}, |
| 55 | { 70, 5}, { 102, 5}, { 134, 6}, { 198, 7}, |
| 56 | {326, 8}, { 582, 9}, {1094, 10}, {2118, 24}, |
| 57 | }; |
| 58 | |
| 59 | static const int kInsertAndCopyRangeLut[9] = { |
| 60 | 0, 1, 4, 2, 3, 6, 5, 7, 8, |
| 61 | }; |
| 62 | |
| 63 | static const int kInsertRangeLut[9] = { |
| 64 | 0, 0, 1, 1, 0, 2, 1, 2, 2, |
| 65 | }; |
| 66 | |
| 67 | static const int kCopyRangeLut[9] = { |
| 68 | 0, 1, 0, 1, 2, 0, 2, 1, 2, |
| 69 | }; |
| 70 | |
| 71 | int InsertLengthPrefix(int length) { |
| 72 | for (int i = 0; i < kNumInsertLenPrefixes; ++i) { |
| 73 | const PrefixCodeRange& range = kInsertLengthPrefixCode[i]; |
| 74 | if (length >= range.offset && length < range.offset + (1 << range.nbits)) { |
| 75 | return i; |
| 76 | } |
| 77 | } |
| 78 | return -1; |
| 79 | } |
| 80 | |
| 81 | int CopyLengthPrefix(int length) { |
| 82 | for (int i = 0; i < kNumCopyLenPrefixes; ++i) { |
| 83 | const PrefixCodeRange& range = kCopyLengthPrefixCode[i]; |
| 84 | if (length >= range.offset && length < range.offset + (1 << range.nbits)) { |
| 85 | return i; |
| 86 | } |
| 87 | } |
| 88 | return -1; |
| 89 | } |
| 90 | |
| 91 | int CommandPrefix(int insert_length, int copy_length) { |
| 92 | if (copy_length == 0) { |
Zoltan Szabadka | e765008 | 2014-03-20 14:32:35 +0100 | [diff] [blame^] | 93 | copy_length = 4; |
Zoltan Szabadka | c66e4e3 | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 94 | } |
| 95 | int insert_prefix = InsertLengthPrefix(insert_length); |
| 96 | int copy_prefix = CopyLengthPrefix(copy_length); |
| 97 | int range_idx = 3 * (insert_prefix >> 3) + (copy_prefix >> 3); |
| 98 | return ((kInsertAndCopyRangeLut[range_idx] << 6) + |
| 99 | ((insert_prefix & 7) << 3) + (copy_prefix & 7)); |
| 100 | } |
| 101 | |
| 102 | int InsertLengthExtraBits(int code) { |
| 103 | int insert_code = (kInsertRangeLut[code >> 6] << 3) + ((code >> 3) & 7); |
| 104 | return kInsertLengthPrefixCode[insert_code].nbits; |
| 105 | } |
| 106 | |
| 107 | int InsertLengthOffset(int code) { |
| 108 | int insert_code = (kInsertRangeLut[code >> 6] << 3) + ((code >> 3) & 7); |
| 109 | return kInsertLengthPrefixCode[insert_code].offset; |
| 110 | } |
| 111 | |
| 112 | int CopyLengthExtraBits(int code) { |
| 113 | int copy_code = (kCopyRangeLut[code >> 6] << 3) + (code & 7); |
| 114 | return kCopyLengthPrefixCode[copy_code].nbits; |
| 115 | } |
| 116 | |
| 117 | int CopyLengthOffset(int code) { |
| 118 | int copy_code = (kCopyRangeLut[code >> 6] << 3) + (code & 7); |
| 119 | return kCopyLengthPrefixCode[copy_code].offset; |
| 120 | } |
| 121 | |
| 122 | void PrefixEncodeCopyDistance(int distance_code, |
| 123 | int num_direct_codes, |
| 124 | int postfix_bits, |
| 125 | uint16_t* code, |
| 126 | int* nbits, |
| 127 | uint32_t* extra_bits) { |
| 128 | distance_code -= 1; |
| 129 | if (distance_code < kNumDistanceShortCodes + num_direct_codes) { |
| 130 | *code = distance_code; |
| 131 | *nbits = 0; |
| 132 | *extra_bits = 0; |
| 133 | return; |
| 134 | } |
| 135 | distance_code -= kNumDistanceShortCodes + num_direct_codes; |
| 136 | distance_code += (1 << (postfix_bits + 2)); |
| 137 | int bucket = Log2Floor(distance_code) - 1; |
| 138 | int postfix_mask = (1 << postfix_bits) - 1; |
| 139 | int postfix = distance_code & postfix_mask; |
| 140 | int prefix = (distance_code >> bucket) & 1; |
| 141 | int offset = (2 + prefix) << bucket; |
| 142 | *nbits = bucket - postfix_bits; |
| 143 | *code = kNumDistanceShortCodes + num_direct_codes + |
| 144 | ((2 * (*nbits - 1) + prefix) << postfix_bits) + postfix; |
| 145 | *extra_bits = (distance_code - offset) >> postfix_bits; |
| 146 | } |
| 147 | |
| 148 | int BlockLengthPrefix(int length) { |
| 149 | for (int i = 0; i < kNumBlockLenPrefixes; ++i) { |
| 150 | const PrefixCodeRange& range = kBlockLengthPrefixCode[i]; |
| 151 | if (length >= range.offset && length < range.offset + (1 << range.nbits)) { |
| 152 | return i; |
| 153 | } |
| 154 | } |
| 155 | return -1; |
| 156 | } |
| 157 | |
| 158 | int BlockLengthExtraBits(int length_code) { |
| 159 | return kBlockLengthPrefixCode[length_code].nbits; |
| 160 | } |
| 161 | |
| 162 | int BlockLengthOffset(int length_code) { |
| 163 | return kBlockLengthPrefixCode[length_code].offset; |
| 164 | } |
| 165 | |
| 166 | } // namespace brotli |