Page Speed Optimization Libraries
1.6.29.3
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00001 /* 00002 * Copyright 2010 Google Inc. 00003 * 00004 * Licensed under the Apache License, Version 2.0 (the "License"); 00005 * you may not use this file except in compliance with the License. 00006 * You may obtain a copy of the License at 00007 * 00008 * http:///www.apache.org/licenses/LICENSE-2.0 00009 * 00010 * Unless required by applicable law or agreed to in writing, software 00011 * distributed under the License is distributed on an "AS IS" BASIS, 00012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 00013 * See the License for the specific language governing permissions and 00014 * limitations under the License. 00015 */ 00017 00018 #ifndef NET_INSTAWEB_UTIL_PUBLIC_ROLLING_HASH_H_ 00019 #define NET_INSTAWEB_UTIL_PUBLIC_ROLLING_HASH_H_ 00020 00021 #include <cstddef> 00022 #include "base/logging.h" 00023 #include "net/instaweb/util/public/basictypes.h" 00024 00025 namespace net_instaweb { 00026 00029 00031 extern const uint64 kRollingHashCharTable[256]; 00032 00034 uint64 RollingHash(const char* buf, size_t start, size_t n); 00035 00045 inline uint64 NextRollingHash( 00046 const char* buf, size_t start, size_t n, uint64 prev) { 00049 CHECK_LT(static_cast<size_t>(0), start); 00050 uint64 start_hash = 00051 kRollingHashCharTable[static_cast<uint8>(buf[start - 1])]; 00052 uint64 end_hash = 00053 kRollingHashCharTable[static_cast<uint8>(buf[start - 1 + n])]; 00054 uint64 prev_rot1 = (prev << 1) | (prev >> 63); 00055 uint64 start_hash_rotn; 00059 size_t shift = n % 64; 00060 if (shift == 0) { 00061 start_hash_rotn = start_hash; 00062 } else { 00064 start_hash_rotn = (start_hash << shift) | (start_hash >> (64 - shift)); 00065 } 00066 return (start_hash_rotn ^ prev_rot1 ^ end_hash); 00067 } 00068 } 00069 00070 #endif ///< NET_INSTAWEB_UTIL_PUBLIC_ROLLING_HASH_H_