Page Speed Optimization Libraries  1.5.27.2
net/instaweb/util/public/rolling_hash.h
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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_
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