libcruft-util/hash/wang.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 2010-2015 Danny Robson <danny@nerdcruft.net>
*/
#ifdef __UTIL_HASH_WANG_IPP
#error
#endif
#define __UTIL_HASH_WANG_IPP
//-----------------------------------------------------------------------------
constexpr uint32_t
util::hash::wang (uint32_t key) {
// a prime or an odd constant
constexpr uint32_t c2 = 0x27d4eb2d;
key = (key ^ 61) ^ (key >> 16);
key = key + (key << 3);
key = key ^ (key >> 4);
key = key * c2;
key = key ^ (key >> 15);
return key;
}
//-----------------------------------------------------------------------------
constexpr uint64_t
util::hash::wang (uint64_t key) {
key = ~key + (key << 21); // key = (key << 21) - key - 1;
key = key ^ (key >> 24);
key = (key + (key << 3)) + (key << 8); // key * 265
key = key ^ (key >> 14);
key = (key + (key << 2)) + (key << 4); // key * 21
key = key ^ (key >> 28);
key = key + (key << 31);
return key;
}