libcruft-util/hash/murmur/murmur1.cpp

64 lines
1.6 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 "murmur1.hpp"
#include "common.hpp"
#include "../../debug.hpp"
//-----------------------------------------------------------------------------
uint32_t
util::hash::murmur1::mix (uint32_t h, uint32_t k)
{
static const uint32_t m = 0xc6a4a793;
h += k;
h *= m;
h ^= h >> 16;
return h;
}
//-----------------------------------------------------------------------------
uint32_t
util::hash::murmur1::hash_32 (const void *restrict data,
size_t len,
uint32_t seed)
{
CHECK (data);
static const uint32_t m = 0xc6a4a793;
uint32_t h = seed ^ (len * m);
// mix the body
auto cursor = reinterpret_cast<const uint32_t*> (data);
auto last = cursor + len / sizeof (uint32_t);
for (; cursor < last; ++cursor)
h = mix (h, *cursor);
// mix the tail
if (len % sizeof (uint32_t))
h = mix (h, murmur::tail (cursor, len));
// finalise
h *= m; h ^= h >> 10;
h *= m; h ^= h >> 17;
return h;
}