libcruft-util/hash/crc.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/.
 *
 * Copyright 2011 Danny Robson <danny@nerdcruft.net>
 */

#include "crc.hpp"

#include "../bitwise.hpp"

#include <array>

using cruft::hash::crc;


///////////////////////////////////////////////////////////////////////////////
template <
    typename DigestT,
    DigestT Generator,
    DigestT Initial,
    DigestT Final,
    bool ReflectIn,
    bool ReflectOut
>
const std::array<DigestT,256>
crc<
    DigestT,Generator,Initial,Final,ReflectIn,ReflectOut
>::s_table = crc<DigestT,Generator,Initial,Final,ReflectIn,ReflectOut>::table ();


///////////////////////////////////////////////////////////////////////////////
template <
    typename DigestT,
    DigestT Generator,
    DigestT Initial,
    DigestT Final,
    bool ReflectIn,
    bool ReflectOut
>
typename crc<DigestT,Generator,Initial,Final,ReflectIn,ReflectOut>::digest_t
crc<
    DigestT,Generator,Initial,Final,ReflectIn,ReflectOut
>::operator() (const cruft::view<const uint8_t*> data) const noexcept
{
    auto accum = Initial;

    for (auto i: data) {
        if (ReflectIn)
            accum = s_table[i ^ (accum & 0xFFu)] ^ (accum >> 8u);
        else {
            constexpr auto shift = sizeof (DigestT) * 8u - 8u;
            accum = (accum << 8u) ^ s_table[(accum >> shift) ^ i];
        }
    }

    return (ReflectIn != ReflectOut ? cruft::reverse (accum) : accum) ^ Final;
}


///////////////////////////////////////////////////////////////////////////////
template <
    typename DigestT,
    DigestT Generator,
    DigestT Initial,
    DigestT Final,
    bool ReflectIn,
    bool ReflectOut
>
constexpr
std::array<DigestT,256>
cruft::hash::crc<
    DigestT,Generator,Initial,Final,ReflectIn,ReflectOut
>::table (void)
{
    // We want to use a std::array here for a (slight) safety advantage, but
    // it means that we have to use calls to array::data instead of operator[]
    // to retain constexpr.
    std::array<digest_t,256> values {};

    if (ReflectIn) {
        constexpr auto gen = cruft::reverse (Generator);

        for (int i = 0; i < 256; ++i) {
            digest_t c = i;

            for (int k = 0; k < 8; ++k) {
                if (c & 1)
                    c = gen ^ (c >> 1);
                else
                    c >>= 1;
            }

            values.data ()[i] = c;
        }
    } else {
        constexpr DigestT   shift =                sizeof (DigestT) * 8u - 8u;
        constexpr DigestT highbit = DigestT(1) << (sizeof (DigestT) * 8u - 1u);

        for (int idx = 0; idx < 256; ++idx) {
            DigestT c = DigestT (idx) << shift;

            for (int i = 0; i < 8; ++i) {
                if (c & highbit)
                    c = (c << DigestT (1)) ^ Generator;
                else
                    c <<= DigestT(1);
            }

            values.data()[idx] = c;
        }
    }

    return values;
};


///////////////////////////////////////////////////////////////////////////////
template class cruft::hash::crc<uint32_t, 0x04C11DB7, 0xffffffff, 0xffffffff, true,  true >; // crc32
template class cruft::hash::crc<uint32_t, 0x04C11DB7, 0xffffffff, 0xffffffff, false, false>; // crc32b
template class cruft::hash::crc<uint32_t, 0x1edc6f41, 0xffffffff, 0xffffffff, true,  true>;  // crc32c
template class cruft::hash::crc<uint32_t, 0xa833982b, 0xffffffff, 0xffffffff, true,  true>;  // crc32d

template class cruft::hash::crc<uint32_t, 0x04C11DB7, 0x00000000, 0x00000000, false, false>; // ogg

template class cruft::hash::crc<uint64_t, 0x42f0e1eba9ea3693, 0, 0, false, false>; // crc64