libcruft-util/hash/crc.hpp

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/*
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* 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
*
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* 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 2011-2018 Danny Robson <danny@nerdcruft.net>
*/
#ifndef CRUFT_UTIL_HASH_CRC_HPP
#define CRUFT_UTIL_HASH_CRC_HPP
#include "../view.hpp"
#include <array>
#include <cstdint>
#include <cstdlib>
#include <type_traits>
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///////////////////////////////////////////////////////////////////////////////
namespace util::hash {
// Implements the crc checksum (from ethernet, png, etc).
//
// Adapted from the PNG specification (ISO/IEC 15948:2003), appendix D and
// the public domain implementation of Ross Williams.
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//
// Generator: the polynomial, with the leading (ie, 32nd) high bit truncated.
// Initial: value used to initialise the digest
// Final: value to xor against the digest at finish time
// ReflectIn: whether to reverse the bits of each data byte
// ReflectOut: whether to reverse the bits of the digest at finish time
//
// Note that reflection isn't necessarily explicitly performed at update
// time. Instead we construct the lookup table appropriately to use the
// data values directly.
template <
typename DigestT,
DigestT Generator,
DigestT Initial,
DigestT Final,
bool ReflectIn,
bool ReflectOut
>
class crc {
public:
using digest_t = DigestT;
static constexpr auto generator = Generator;
digest_t operator() (util::view<const uint8_t*>) const noexcept;
static constexpr
std::array<DigestT,256>
table (void);
private:
static const std::array<DigestT,256> s_table;
};
using crc32 = crc<uint32_t, 0x04c11db7, 0xffffffff, 0xffffffff, true, true>;
using crc32b = crc<uint32_t, 0x04c11db7, 0xffffffff, 0xffffffff, false, false>;
using crc32c = crc<uint32_t, 0x1edc6f41, 0xffffffff, 0xffffffff, true, true>;
using crc32d = crc<uint32_t, 0xa833982b, 0xffffffff, 0xffffffff, true, true>;
using crc64 = crc<uint64_t, 0x42f0e1eba9ea3693, 0, 0, false, false>;
}
#endif