70 lines
2.2 KiB
C++
70 lines
2.2 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2011-2018 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef CRUFT_UTIL_HASH_CRC_HPP
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#define CRUFT_UTIL_HASH_CRC_HPP
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#include "../view.hpp"
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#include <array>
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#include <cstdint>
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#include <cstdlib>
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#include <type_traits>
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///////////////////////////////////////////////////////////////////////////////
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namespace cruft::hash {
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// Implements the crc checksum (from ethernet, png, etc).
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//
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// Adapted from the PNG specification (ISO/IEC 15948:2003), appendix D and
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// the public domain implementation of Ross Williams.
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//
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// Generator: the polynomial, with the leading (ie, 32nd) high bit truncated.
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// Initial: value used to initialise the digest
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// Final: value to xor against the digest at finish time
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// ReflectIn: whether to reverse the bits of each data byte
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// ReflectOut: whether to reverse the bits of the digest at finish time
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//
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// Note that reflection isn't necessarily explicitly performed at update
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// time. Instead we construct the lookup table appropriately to use the
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// data values directly.
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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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class crc {
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public:
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using digest_t = DigestT;
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static constexpr auto generator = Generator;
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digest_t operator() (cruft::view<const uint8_t*>) const noexcept;
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static constexpr
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std::array<DigestT,256>
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table (void);
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private:
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static const std::array<DigestT,256> s_table;
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};
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using crc32 = crc<uint32_t, 0x04c11db7, 0xffffffff, 0xffffffff, true, true>;
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using crc32b = crc<uint32_t, 0x04c11db7, 0xffffffff, 0xffffffff, false, false>;
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using crc32c = crc<uint32_t, 0x1edc6f41, 0xffffffff, 0xffffffff, true, true>;
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using crc32d = crc<uint32_t, 0xa833982b, 0xffffffff, 0xffffffff, true, true>;
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using crc64 = crc<uint64_t, 0x42f0e1eba9ea3693, 0, 0, false, false>;
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}
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#endif
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