mirror of
https://github.com/google/brotli.git
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88 lines
2.7 KiB
C++
88 lines
2.7 KiB
C++
// Copyright 2010 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// Function to find maximal matching prefixes of strings.
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#ifndef BROTLI_ENC_FIND_MATCH_LENGTH_H_
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#define BROTLI_ENC_FIND_MATCH_LENGTH_H_
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#include <stdint.h>
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#include <stddef.h>
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#include "./port.h"
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namespace brotli {
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// Separate implementation for little-endian 64-bit targets, for speed.
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#if defined(__GNUC__) && defined(_LP64) && defined(IS_LITTLE_ENDIAN)
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static inline int FindMatchLengthWithLimit(const uint8_t* s1,
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const uint8_t* s2,
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size_t limit) {
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int matched = 0;
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size_t limit2 = (limit >> 3) + 1; // + 1 is for pre-decrement in while
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while (PREDICT_TRUE(--limit2)) {
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if (PREDICT_FALSE(BROTLI_UNALIGNED_LOAD64(s2) ==
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BROTLI_UNALIGNED_LOAD64(s1 + matched))) {
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s2 += 8;
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matched += 8;
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} else {
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uint64_t x =
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BROTLI_UNALIGNED_LOAD64(s2) ^ BROTLI_UNALIGNED_LOAD64(s1 + matched);
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int matching_bits = __builtin_ctzll(x);
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matched += matching_bits >> 3;
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return matched;
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}
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}
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limit = (limit & 7) + 1; // + 1 is for pre-decrement in while
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while (--limit) {
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if (PREDICT_TRUE(s1[matched] == *s2)) {
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++s2;
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++matched;
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} else {
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return matched;
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}
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}
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return matched;
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}
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#else
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static inline int FindMatchLengthWithLimit(const uint8_t* s1,
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const uint8_t* s2,
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size_t limit) {
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int matched = 0;
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const uint8_t* s2_limit = s2 + limit;
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const uint8_t* s2_ptr = s2;
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// Find out how long the match is. We loop over the data 32 bits at a
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// time until we find a 32-bit block that doesn't match; then we find
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// the first non-matching bit and use that to calculate the total
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// length of the match.
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while (s2_ptr <= s2_limit - 4 &&
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BROTLI_UNALIGNED_LOAD32(s2_ptr) ==
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BROTLI_UNALIGNED_LOAD32(s1 + matched)) {
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s2_ptr += 4;
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matched += 4;
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}
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while ((s2_ptr < s2_limit) && (s1[matched] == *s2_ptr)) {
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++s2_ptr;
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++matched;
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}
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return matched;
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}
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#endif
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} // namespace brotli
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#endif // BROTLI_ENC_FIND_MATCH_LENGTH_H_
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