1 /* Copyright 2010 Google Inc. All Rights Reserved. 2 3 Distributed under MIT license. 4 See file LICENSE for detail or copy at https://opensource.org/licenses/MIT 5 */ 6 7 /* Function to find maximal matching prefixes of strings. */ 8 9 #ifndef BROTLI_ENC_FIND_MATCH_LENGTH_H_ 10 #define BROTLI_ENC_FIND_MATCH_LENGTH_H_ 11 12 #include <brotli/types.h> 13 #include "./port.h" 14 15 #if defined(__cplusplus) || defined(c_plusplus) 16 extern "C" { 17 #endif 18 19 /* Separate implementation for little-endian 64-bit targets, for speed. */ 20 #if defined(__GNUC__) && defined(_LP64) && defined(IS_LITTLE_ENDIAN) 21 FindMatchLengthWithLimit(const uint8_t * s1,const uint8_t * s2,size_t limit)22static BROTLI_INLINE size_t FindMatchLengthWithLimit(const uint8_t* s1, 23 const uint8_t* s2, 24 size_t limit) { 25 size_t matched = 0; 26 size_t limit2 = (limit >> 3) + 1; /* + 1 is for pre-decrement in while */ 27 while (BROTLI_PREDICT_TRUE(--limit2)) { 28 if (BROTLI_PREDICT_FALSE(BROTLI_UNALIGNED_LOAD64(s2) == 29 BROTLI_UNALIGNED_LOAD64(s1 + matched))) { 30 s2 += 8; 31 matched += 8; 32 } else { 33 uint64_t x = 34 BROTLI_UNALIGNED_LOAD64(s2) ^ BROTLI_UNALIGNED_LOAD64(s1 + matched); 35 size_t matching_bits = (size_t)__builtin_ctzll(x); 36 matched += matching_bits >> 3; 37 return matched; 38 } 39 } 40 limit = (limit & 7) + 1; /* + 1 is for pre-decrement in while */ 41 while (--limit) { 42 if (BROTLI_PREDICT_TRUE(s1[matched] == *s2)) { 43 ++s2; 44 ++matched; 45 } else { 46 return matched; 47 } 48 } 49 return matched; 50 } 51 #else 52 static BROTLI_INLINE size_t FindMatchLengthWithLimit(const uint8_t* s1, 53 const uint8_t* s2, 54 size_t limit) { 55 size_t matched = 0; 56 const uint8_t* s2_limit = s2 + limit; 57 const uint8_t* s2_ptr = s2; 58 /* Find out how long the match is. We loop over the data 32 bits at a 59 time until we find a 32-bit block that doesn't match; then we find 60 the first non-matching bit and use that to calculate the total 61 length of the match. */ 62 while (s2_ptr <= s2_limit - 4 && 63 BROTLI_UNALIGNED_LOAD32(s2_ptr) == 64 BROTLI_UNALIGNED_LOAD32(s1 + matched)) { 65 s2_ptr += 4; 66 matched += 4; 67 } 68 while ((s2_ptr < s2_limit) && (s1[matched] == *s2_ptr)) { 69 ++s2_ptr; 70 ++matched; 71 } 72 return matched; 73 } 74 #endif 75 76 #if defined(__cplusplus) || defined(c_plusplus) 77 } /* extern "C" */ 78 #endif 79 80 #endif /* BROTLI_ENC_FIND_MATCH_LENGTH_H_ */ 81