libcruft-util/hash/fnv1a.cpp

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/*
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* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
* Copyright 2010-2015 Danny Robson <danny@nerdcruft.net>
*/
#include "fnv1a.hpp"
using cruft::hash::fnv1a;
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///////////////////////////////////////////////////////////////////////////////
// Prime is,
// 32: 2^ 24 + 2^8 + 0x93
// 64: 2^ 40 + 2^8 + 0xb3
// 128: 2^ 88 + 2^8 + 0x3B
// 256: 2^168 + 2^8 + 0x63
// 512: 2^344 + 2^8 + 0x57
// 1024: 2^680 + 2^8 + 0x8D
//
// Bias is the FNV-0 hash of "chongo <Landon Curt Noll> /\\../\\"
template <typename DigestT>
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struct constants { };
//-----------------------------------------------------------------------------
template <>
struct constants<uint32_t> {
static constexpr uint32_t prime = 16777619u;
static constexpr uint32_t bias = 2166136261u;
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};
//-----------------------------------------------------------------------------
template <>
struct constants<uint64_t> {
static constexpr uint64_t prime = 1099511628211u;
static constexpr uint64_t bias = 14695981039346656037u;
};
///////////////////////////////////////////////////////////////////////////////
template <typename DigestT>
typename fnv1a<DigestT>::digest_t
fnv1a<DigestT>::operator() (const cruft::view<const uint8_t*> data) const noexcept
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{
auto result = constants<DigestT>::bias;
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for (auto i: data) {
result ^= i;
result *= constants<DigestT>::prime;
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}
return result;
}
template struct cruft::hash::fnv1a<uint32_t>;
template struct cruft::hash::fnv1a<uint64_t>;