libcruft-util/hash/murmur/murmur2.hpp
Danny Robson f6056153e3 rename root namespace from util to cruft
This places, at long last, the core library code into the same namespace
as the extended library code.
2018-08-05 14:42:02 +10:00

86 lines
2.0 KiB
C++

/*
* 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/.
*
* Copyright 2015 Danny Robson <danny@nerdcruft.net>
*/
#ifndef __UTIL_HASH_MURMUR_MURMUR2_HPP
#define __UTIL_HASH_MURMUR_MURMUR2_HPP
#include "../../view.hpp"
#include <cstddef>
#include <cstdint>
// Austin Appleby's MumurHash2, and MurmurHash64A. The exhaustive list of
// variants is deliberately not provided. You can damn well align your data or
// fix the algorithm.
namespace cruft::hash {
namespace detail::murmur2 {
template <typename T> struct constants;
template <>
struct constants<uint32_t> {
static const uint32_t m = 0x5bd1e995;
static const int32_t r = 24;
};
template <>
struct constants<uint64_t> {
static const uint64_t m = 0xc6a4a7935bd1e995;
static const int64_t r = 47;
};
}
template <typename DigestT>
class murmur2 {
public:
using digest_t = DigestT;
using seed_t = DigestT;
murmur2 (seed_t _seed):
m_seed (_seed)
{ ; }
static constexpr uint32_t mix (uint32_t h, uint32_t k)
{
constexpr uint32_t m = detail::murmur2::constants<uint32_t>::m;
constexpr uint32_t r = detail::murmur2::constants<uint32_t>::r;
k *= m;
k ^= k >> r;
k *= m;
h *= m;
h ^= k;
return h;
}
static constexpr uint64_t mix (uint64_t h, uint64_t k)
{
constexpr uint64_t m = detail::murmur2::constants<uint64_t>::m;
constexpr uint64_t r = detail::murmur2::constants<uint64_t>::r;
k *= m;
k ^= k >> r;
k *= m;
h ^= k;
h *= m;
return h;
}
digest_t operator() (cruft::view<const uint8_t*> data) const noexcept;
private:
seed_t m_seed;
};
}
#endif