71 lines
2.0 KiB
C++
71 lines
2.0 KiB
C++
/*
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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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* Copyright 2010-2015 Danny Robson <danny@nerdcruft.net>
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*/
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#include "fnv1a.hpp"
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using util::hash::fnv1a;
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///////////////////////////////////////////////////////////////////////////////
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// Prime is,
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// 32: 2^ 24 + 2^8 + 0x93
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// 64: 2^ 40 + 2^8 + 0xb3
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// 128: 2^ 88 + 2^8 + 0x3B
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// 256: 2^168 + 2^8 + 0x63
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// 512: 2^344 + 2^8 + 0x57
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// 1024: 2^680 + 2^8 + 0x8D
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//
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// Bias is the FNV-0 hash of "chongo <Landon Curt Noll> /\\../\\"
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template <typename DigestT>
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struct constants { };
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//-----------------------------------------------------------------------------
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template <>
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struct constants<uint32_t> {
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static constexpr uint32_t prime = 16777619u;
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static constexpr uint32_t bias = 2166136261u;
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};
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//-----------------------------------------------------------------------------
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template <>
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struct constants<uint64_t> {
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static constexpr uint64_t prime = 1099511628211u;
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static constexpr uint64_t bias = 14695981039346656037u;
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};
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///////////////////////////////////////////////////////////////////////////////
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template <typename DigestT>
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typename fnv1a<DigestT>::digest_t
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fnv1a<DigestT>::operator() (const util::view<const uint8_t*> data) const noexcept
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{
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auto result = constants<DigestT>::bias;
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for (auto i: data) {
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result ^= i;
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result *= constants<DigestT>::prime;
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}
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return result;
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}
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template struct util::hash::fnv1a<uint32_t>;
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template struct util::hash::fnv1a<uint64_t>;
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