00001
00002
00003
00004
00005
00006
00007
00008
00009
00010
00011
00012
00013
00014
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_