libcruft-util/hash/murmur/murmur2.cpp

90 lines
2.3 KiB
C++

/*
* 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 2015 Danny Robson <danny@nerdcruft.net>
*/
#include "murmur2.hpp"
#include "../../debug.hpp"
#include "common.hpp"
///////////////////////////////////////////////////////////////////////////////
uint32_t
util::hash::murmur2::hash_32 (const void *restrict key,
size_t len,
uint32_t seed)
{
CHECK (key);
// setup
constexpr auto m = detail::constants<uint32_t>::m;
uint32_t h = seed ^ (len & 0xffffffff);
// body
auto cursor = reinterpret_cast<const uint32_t*> (key);
auto last = cursor + len / sizeof (uint32_t);
for (; cursor < last; ++cursor)
h = mix (h, *cursor);
// tail
if (len % sizeof (uint32_t)) {
h ^= murmur::tail<uint32_t> (reinterpret_cast<const uint8_t*> (cursor), len);
h *= m;
}
// finalise
h ^= h >> 13;
h *= m;
h ^= h >> 15;
return h;
}
//-----------------------------------------------------------------------------
uint64_t
util::hash::murmur2::hash_64 (const void *restrict key,
size_t len,
uint64_t seed)
{
// setup
constexpr auto m = detail::constants<uint64_t>::m;
constexpr auto r = detail::constants<uint64_t>::r;
uint64_t h = seed ^ (len * m);
// body
auto cursor = reinterpret_cast<const uint64_t*> (key);
auto last = cursor + len / sizeof (uint64_t);
for (; cursor < last; ++cursor)
h = mix (h, *cursor);
// tail
if (len % sizeof (uint64_t)) {
h ^= murmur::tail<uint64_t> (reinterpret_cast<const uint8_t*> (cursor), len);
h *= m;
}
// finalise
h ^= h >> r;
h *= m;
h ^= h >> r;
return h;
}