libcruft-util/noise/rand/hash.ipp

75 lines
2.1 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>
*/
#ifdef __UTIL_NOISE_RAND_HASH_IPP
#error
#endif
#define __UTIL_NOISE_RAND_HASH_IPP
namespace util { namespace noise { namespace rand {
//-------------------------------------------------------------------------
template <
typename U,
size_t S,
typename T,
template <size_t,typename> class Q
>
U
hash::scalar (uint64_t seed, Q<S,T> query) noexcept
{
constexpr decltype(seed) BITS = 0xFFFF;
static_assert (std::is_integral<T>::value,
"mixing only works on integral types");
uint64_t accum = seed;
for (auto i: query)
accum = util::hash::murmur2::mix (accum, i);
return (accum & BITS) / U{BITS};
}
//-------------------------------------------------------------------------
template <
template <size_t,typename> class R,
typename U,
size_t S,
typename T,
template <size_t,typename> class Q
>
R<S,U>
hash::coord (uint64_t seed, Q<S,T> query) noexcept
{
constexpr decltype(seed) PERTURB = 0x96c39996c36c36c3;
constexpr decltype(seed) BITS = 0xFFFF;
auto accum = seed ^ PERTURB;
for (auto i: query)
accum = util::hash::murmur2::mix (accum, i);
R<S,U> result;
for (auto &i: result) {
i = (accum & BITS);
i /= BITS;
accum = util::hash::murmur2::mix (accum, seed);
}
return result;
}
} } }