libcruft-util/hash/murmur/murmur2.cpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 * limitations under the License.
 *
 * Copyright 2015 Danny Robson <danny@nerdcruft.net>
 */

#include "murmur2.hpp"

#include "common.hpp"

#include "../../debug/panic.hpp"

using cruft::hash::murmur2;


///////////////////////////////////////////////////////////////////////////////
static uint32_t
hash_32 (const void *restrict key,
                           size_t len,
                           uint32_t seed)
{
    // setup
    constexpr auto m = cruft::hash::detail::murmur2::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 = cruft::hash::murmur2<uint32_t>::mix (h, *cursor);

    // tail
    if (len % sizeof (uint32_t)) {
        h ^= cruft::hash::murmur::tail<uint32_t> (reinterpret_cast<const uint8_t*> (cursor), len);
        h *= m;
    }

    // finalise
    h ^= h >> 13;
    h *= m;
    h ^= h >> 15;

    return h;
}


//-----------------------------------------------------------------------------
static uint64_t
hash_64 (const void *restrict key,
                           size_t len,
                           uint64_t seed)
{
    // setup
    constexpr auto m = cruft::hash::detail::murmur2::constants<uint64_t>::m;
    constexpr auto r = cruft::hash::detail::murmur2::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 = cruft::hash::murmur2<uint64_t>::mix (h, *cursor);

    // tail
    if (len % sizeof (uint64_t)) {
        h ^= cruft::hash::murmur::tail<uint64_t> (reinterpret_cast<const uint8_t*> (cursor), len);
        h *= m;
    }

    // finalise
    h ^= h >> r;
    h *= m;
    h ^= h >> r;

    return h;
}


///////////////////////////////////////////////////////////////////////////////
template <typename DigestT>
typename murmur2<DigestT>::digest_t
murmur2<DigestT>::operator() (cruft::view<const uint8_t*> data) const noexcept
{
    static_assert (std::is_same_v<DigestT,uint32_t> || std::is_same_v<DigestT,uint64_t>);

    if constexpr (std::is_same_v<DigestT,uint32_t>) {
        return hash_32 (data.data (), data.size (), m_seed);
    }

    if constexpr (std::is_same_v<DigestT,uint64_t>) {
        return hash_64 (data.data (), data.size (), m_seed);
    }

    unreachable ();
}


///////////////////////////////////////////////////////////////////////////////
template class cruft::hash::murmur2<uint32_t>;
template class cruft::hash::murmur2<uint64_t>;