128 lines
3.5 KiB
C++
128 lines
3.5 KiB
C++
/*
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* Copyright 2015 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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#ifndef FLATBUFFERS_HASH_H_
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#define FLATBUFFERS_HASH_H_
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#include <cstdint>
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#include <cstring>
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#include "flatbuffers/flatbuffers.h"
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namespace flatbuffers {
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template<typename T> struct FnvTraits {
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static const T kFnvPrime;
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static const T kOffsetBasis;
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};
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template<> struct FnvTraits<uint32_t> {
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static const uint32_t kFnvPrime = 0x01000193;
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static const uint32_t kOffsetBasis = 0x811C9DC5;
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};
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template<> struct FnvTraits<uint64_t> {
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static const uint64_t kFnvPrime = 0x00000100000001b3ULL;
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static const uint64_t kOffsetBasis = 0xcbf29ce484222645ULL;
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};
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template<typename T> T HashFnv1(const char *input) {
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T hash = FnvTraits<T>::kOffsetBasis;
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for (const char *c = input; *c; ++c) {
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hash *= FnvTraits<T>::kFnvPrime;
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hash ^= static_cast<unsigned char>(*c);
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}
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return hash;
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}
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template<typename T> T HashFnv1a(const char *input) {
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T hash = FnvTraits<T>::kOffsetBasis;
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for (const char *c = input; *c; ++c) {
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hash ^= static_cast<unsigned char>(*c);
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hash *= FnvTraits<T>::kFnvPrime;
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}
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return hash;
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}
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template<> inline uint16_t HashFnv1<uint16_t>(const char *input) {
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uint32_t hash = HashFnv1<uint32_t>(input);
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return (hash >> 16) ^ (hash & 0xffff);
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}
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template<> inline uint16_t HashFnv1a<uint16_t>(const char *input) {
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uint32_t hash = HashFnv1a<uint32_t>(input);
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return (hash >> 16) ^ (hash & 0xffff);
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}
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template<typename T> struct NamedHashFunction {
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const char *name;
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typedef T (*HashFunction)(const char *);
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HashFunction function;
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};
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const NamedHashFunction<uint16_t> kHashFunctions16[] = {
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{ "fnv1_16", HashFnv1<uint16_t> },
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{ "fnv1a_16", HashFnv1a<uint16_t> },
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};
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const NamedHashFunction<uint32_t> kHashFunctions32[] = {
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{ "fnv1_32", HashFnv1<uint32_t> },
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{ "fnv1a_32", HashFnv1a<uint32_t> },
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};
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const NamedHashFunction<uint64_t> kHashFunctions64[] = {
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{ "fnv1_64", HashFnv1<uint64_t> },
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{ "fnv1a_64", HashFnv1a<uint64_t> },
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};
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inline NamedHashFunction<uint16_t>::HashFunction FindHashFunction16(
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const char *name) {
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std::size_t size = sizeof(kHashFunctions16) / sizeof(kHashFunctions16[0]);
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for (std::size_t i = 0; i < size; ++i) {
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if (std::strcmp(name, kHashFunctions16[i].name) == 0) {
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return kHashFunctions16[i].function;
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}
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}
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return nullptr;
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}
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inline NamedHashFunction<uint32_t>::HashFunction FindHashFunction32(
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const char *name) {
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std::size_t size = sizeof(kHashFunctions32) / sizeof(kHashFunctions32[0]);
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for (std::size_t i = 0; i < size; ++i) {
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if (std::strcmp(name, kHashFunctions32[i].name) == 0) {
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return kHashFunctions32[i].function;
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}
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}
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return nullptr;
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}
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inline NamedHashFunction<uint64_t>::HashFunction FindHashFunction64(
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const char *name) {
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std::size_t size = sizeof(kHashFunctions64) / sizeof(kHashFunctions64[0]);
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for (std::size_t i = 0; i < size; ++i) {
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if (std::strcmp(name, kHashFunctions64[i].name) == 0) {
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return kHashFunctions64[i].function;
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}
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}
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return nullptr;
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}
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} // namespace flatbuffers
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#endif // FLATBUFFERS_HASH_H_
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