136 lines
4.0 KiB
C++
136 lines
4.0 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2011 Danny Robson <danny@nerdcruft.net>
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*/
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#include "crc.hpp"
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#include "../bitwise.hpp"
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#include "../debug.hpp"
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#include <array>
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using util::hash::crc;
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///////////////////////////////////////////////////////////////////////////////
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template <
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typename DigestT,
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DigestT Generator,
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DigestT Initial,
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DigestT Final,
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bool ReflectIn,
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bool ReflectOut
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>
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const std::array<DigestT,256>
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crc<
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DigestT,Generator,Initial,Final,ReflectIn,ReflectOut
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>::s_table = crc<DigestT,Generator,Initial,Final,ReflectIn,ReflectOut>::table ();
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///////////////////////////////////////////////////////////////////////////////
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template <
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typename DigestT,
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DigestT Generator,
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DigestT Initial,
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DigestT Final,
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bool ReflectIn,
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bool ReflectOut
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>
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typename crc<DigestT,Generator,Initial,Final,ReflectIn,ReflectOut>::digest_t
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crc<
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DigestT,Generator,Initial,Final,ReflectIn,ReflectOut
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>::operator() (const util::view<const uint8_t*> data) const noexcept
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{
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auto accum = Initial;
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for (auto i: data) {
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if (ReflectIn)
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accum = s_table[i ^ (accum & 0xFFu)] ^ (accum >> 8u);
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else {
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constexpr auto shift = sizeof (DigestT) * 8u - 8u;
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accum = (accum << 8u) ^ s_table[(accum >> shift) ^ i];
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}
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}
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return (ReflectIn != ReflectOut ? util::reverse (accum) : accum) ^ Final;
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}
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///////////////////////////////////////////////////////////////////////////////
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template <
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typename DigestT,
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DigestT Generator,
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DigestT Initial,
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DigestT Final,
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bool ReflectIn,
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bool ReflectOut
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>
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constexpr
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std::array<DigestT,256>
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util::hash::crc<
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DigestT,Generator,Initial,Final,ReflectIn,ReflectOut
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>::table (void)
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{
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// We want to use a std::array here for a (slight) safety advantage, but
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// it means that we have to use calls to array::data instead of operator[]
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// to retain constexpr.
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std::array<digest_t,256> values {};
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if (ReflectIn) {
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constexpr auto gen = util::reverse (Generator);
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for (int i = 0; i < 256; ++i) {
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digest_t c = i;
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for (int k = 0; k < 8; ++k) {
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if (c & 1)
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c = gen ^ (c >> 1);
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else
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c >>= 1;
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}
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values.data ()[i] = c;
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}
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} else {
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constexpr DigestT shift = sizeof (DigestT) * 8u - 8u;
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constexpr DigestT highbit = DigestT(1) << (sizeof (DigestT) * 8u - 1u);
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for (int idx = 0; idx < 256; ++idx) {
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DigestT c = DigestT (idx) << shift;
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for (int i = 0; i < 8; ++i) {
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if (c & highbit)
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c = (c << DigestT (1)) ^ Generator;
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else
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c <<= DigestT(1);
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}
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values.data()[idx] = c;
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}
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}
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return values;
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};
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///////////////////////////////////////////////////////////////////////////////
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template class util::hash::crc<uint32_t, 0x04C11DB7, 0xffffffff, 0xffffffff, true, true >; // crc32
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template class util::hash::crc<uint32_t, 0x04C11DB7, 0xffffffff, 0xffffffff, false, false>; // crc32b
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template class util::hash::crc<uint32_t, 0x1edc6f41, 0xffffffff, 0xffffffff, true, true>; // crc32c
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template class util::hash::crc<uint32_t, 0xa833982b, 0xffffffff, 0xffffffff, true, true>; // crc32d
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template class util::hash::crc<uint32_t, 0x04C11DB7, 0x00000000, 0x00000000, false, false>; // ogg
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template class util::hash::crc<uint64_t, 0x42f0e1eba9ea3693, 0, 0, false, false>; // crc64
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