libcruft-util/hash/xxhash.cpp

/*
 * 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 2016 Danny Robson <danny@nerdcruft.net>
 */

#include "./xxhash.hpp"

#include "./debug.hpp"
#include "./bitwise.hpp"
#include "./endian.hpp"

#include <cstring>

using util::hash::xxhash;


///////////////////////////////////////////////////////////////////////////////
template <typename T>
static
T
read_le (const void *ptr)
{
    return *static_cast<const T*> (ptr);
}


///////////////////////////////////////////////////////////////////////////////
template <typename T>
struct constants {
    static const T prime[5];
    static const T round_rotl;
};


//-----------------------------------------------------------------------------
template <>
const uint32_t
constants<uint32_t>::prime[5] = {
        2654435761u,
        2246822519u,
        3266489917u,
         668265263u,
         374761393u,
};


//-----------------------------------------------------------------------------
template <>
const uint32_t
constants<uint32_t>::round_rotl = 13;


//-----------------------------------------------------------------------------
template <>
const uint64_t constants<uint64_t>::prime[5] = {
    11400714785074694791u,
    14029467366897019727u,
     1609587929392839161u,
     9650029242287828579u,
     2870177450012600261u,
};


//-----------------------------------------------------------------------------
template <>
const uint64_t
constants<uint64_t>::round_rotl = 31;


///////////////////////////////////////////////////////////////////////////////
constexpr uint32_t DEFAULT_SEED = 0;


//-----------------------------------------------------------------------------
template <typename T>
xxhash<T>::xxhash (void):
    xxhash (DEFAULT_SEED)
{ ; }


//-----------------------------------------------------------------------------
template <typename T>
xxhash<T>::xxhash (uint32_t _seed):
    m_seed  (_seed)
{
    reset ();
}


//-----------------------------------------------------------------------------
template <typename T>
void
xxhash<T>::reset (void)
{
    memset (&m_state, 0, sizeof (m_state));

    m_state.v1 = m_seed + constants<T>::prime[0] + constants<T>::prime[1];
    m_state.v2 = m_seed + constants<T>::prime[1];
    m_state.v3 = m_seed;
    m_state.v4 = m_seed - constants<T>::prime[0];
}


///////////////////////////////////////////////////////////////////////////////
template <typename T>
static
T
round (T seed, T input)
{
    seed += input * constants<T>::prime[1];
    seed  = util::rotatel (seed, constants<T>::round_rotl);
    seed *= constants<T>::prime[0];

    return seed;
}


///////////////////////////////////////////////////////////////////////////////
template <typename T>
void
xxhash<T>::update (const uint8_t *restrict first, const uint8_t *restrict last)
{
    CHECK (first);
    CHECK (last);
    CHECK_LE (first, last);

    //auto endian = XXH_littleEndian;
    size_t len = last - first;
    auto input = (const void*)first;

    auto          p = reinterpret_cast<const uint8_t*> (input);
    auto const bEnd = p + len;

    constexpr auto CHUNK = 4 * sizeof (T);

    m_state.total_len_32 += (unsigned)len;
    m_state.large_len |= (len >= CHUNK) | (m_state.total_len_32 >= CHUNK);

    if (m_state.memsize + len < CHUNK)  {   /* fill in tmp buffer */
        memcpy ((uint8_t*)(m_state.mem32) + m_state.memsize, input, len);
        m_state.memsize += (unsigned)len;
        return;
    }

    if (m_state.memsize) {   /* some data left from previous update */
        memcpy ((uint8_t*)(m_state.mem32) + m_state.memsize, input, CHUNK - m_state.memsize);
        {   const uint32_t* p32 = m_state.mem32;
            m_state.v1 = round<T> (m_state.v1, ltoh (*p32)); p32++;
            m_state.v2 = round<T> (m_state.v2, ltoh (*p32)); p32++;
            m_state.v3 = round<T> (m_state.v3, ltoh (*p32)); p32++;
            m_state.v4 = round<T> (m_state.v4, ltoh (*p32)); p32++;
        }
        p += CHUNK - m_state.memsize;
        m_state.memsize = 0;
    }

    if (p <= bEnd - CHUNK * sizeof (T)) {
        const uint8_t* const limit = bEnd - 4 * sizeof (T);
        T v1 = m_state.v1;
        T v2 = m_state.v2;
        T v3 = m_state.v3;
        T v4 = m_state.v4;

        do {
            v1 = round<T> (v1, read_le<T> (p)); p += sizeof (T);
            v2 = round<T> (v2, read_le<T> (p)); p += sizeof (T);
            v3 = round<T> (v3, read_le<T> (p)); p += sizeof (T);
            v4 = round<T> (v4, read_le<T> (p)); p += sizeof (T);
        } while (p <= limit);

        m_state.v1 = v1;
        m_state.v2 = v2;
        m_state.v3 = v3;
        m_state.v4 = v4;
    }

    if (p < bEnd) {
        memcpy (m_state.mem32, p, (size_t)(bEnd-p));
        m_state.memsize = (unsigned)(bEnd-p);
    }
}


///////////////////////////////////////////////////////////////////////////////
template <typename T>
void
xxhash<T>::finish (void)
{
    ;
}


///////////////////////////////////////////////////////////////////////////////
template <typename T>
typename xxhash<T>::digest_t
xxhash<T>::digest (void) const
{
    auto p = reinterpret_cast<const uint8_t*> (m_state.mem32);
    auto last = p + m_state.memsize;

    T h;

    if (m_state.large_len) {
        h = rotatel (m_state.v1, T{ 1}) +
            rotatel (m_state.v2, T{ 7}) +
            rotatel (m_state.v3, T{12}) +
            rotatel (m_state.v4, T{18});
    } else {
        h = m_state.v3 /* == seed */ + constants<T>::prime[4];
    }

    h += m_state.total_len_32;

    while (p + sizeof (T) <= last) {
        h += read_le<T> (p)  * constants<T>::prime[2];
        h  = rotatel (h, 17) * constants<T>::prime[3];
        p += 4;
    }

    while (p < last) {
        h += (*p) * constants<T>::prime[4];
        h  = rotatel (h, 11) * constants<T>::prime[0];
        p++;
    }

    h ^= h >> 15; h *= constants<T>::prime[1];
    h ^= h >> 13; h *= constants<T>::prime[2];
    h ^= h >> 16;

    return h;
}


///////////////////////////////////////////////////////////////////////////////
template class util::hash::xxhash<uint32_t>;
template class util::hash::xxhash<uint64_t>;