libcruft-util/hash/murmur/murmur2.ipp

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/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright 2016 Danny Robson <danny@nerdcruft.net>
*/
#if defined(__UTIL_HASH_MURMUR_MURMUR2_IPP)
#error
#endif
#define __UTIL_HASH_MURMUR_MURMUR2_IPP
///////////////////////////////////////////////////////////////////////////////
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namespace util::hash::murmur2::detail {
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;
};
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}
/////////////////////////////////////////////////////////////////////
constexpr uint32_t
util::hash::murmur2::mix (uint32_t h, uint32_t k)
{
constexpr uint32_t m = detail::constants<uint32_t>::m;
constexpr uint32_t r = detail::constants<uint32_t>::r;
k *= m;
k ^= k >> r;
k *= m;
h *= m;
h ^= k;
return h;
}
//-----------------------------------------------------------------------------
// 64 bit murmur2 mixing function. Note the last two lines are swapped
// compared with 32 bit murmur2_mix. It's not clear if this is deliberate
// in the canonical implementation, so we just leave it to help compatibility.
constexpr uint64_t
util::hash::murmur2::mix (uint64_t h, uint64_t k)
{
constexpr uint64_t m = detail::constants<uint64_t>::m;
constexpr uint64_t r = detail::constants<uint64_t>::r;
k *= m;
k ^= k >> r;
k *= m;
h ^= k;
h *= m;
return h;
}