libcruft-util/hash/crc.cpp

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/*
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* 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/.
*
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* Copyright 2011 Danny Robson <danny@nerdcruft.net>
*/
#include "crc.hpp"
#include "../bitwise.hpp"
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#include "../debug.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)
{
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// 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