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◆ main openmsx / src / utils / xxhash.hh
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/*
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   This code is a based on xxhash, the main modifications are:
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    - allow to produce case-insensitive (for ascii) hash values
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    - tweak interface to fit openMSX (e.g. directly work on string_view)
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- - - - - - - - - - - - - - - - - - - -
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 original header:
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   xxHash - Fast Hash algorithm
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   Header File
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   Copyright (C) 2012-2014, Yann Collet.
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   BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
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   Redistribution and use in source and binary forms, with or without
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   modification, are permitted provided that the following conditions are
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   met:
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       * Redistributions of source code must retain the above copyright
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   notice, this list of conditions and the following disclaimer.
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       * Redistributions in binary form must reproduce the above
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   copyright notice, this list of conditions and the following disclaimer
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   in the documentation and/or other materials provided with the
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   distribution.
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   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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   You can contact the author at :
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   - xxHash source repository : http://code.google.com/p/xxhash/
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*/
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#ifndef XXHASH_HH
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#define XXHASH_HH
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#include <bit>
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#include <cassert>
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#include <cstdint>
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#include <cstring>
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#include <string_view>
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inline constexpr uint32_t PRIME32_1 = 2654435761;
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inline constexpr uint32_t PRIME32_2 = 2246822519;
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inline constexpr uint32_t PRIME32_3 = 3266489917;
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inline constexpr uint32_t PRIME32_4 =  668265263;
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inline constexpr uint32_t PRIME32_5 =  374761393;
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template<bool ALIGNED>
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[[nodiscard]] inline uint32_t read32(const uint8_t* ptr)
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{
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	if constexpr (ALIGNED) {
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#ifdef DEBUG
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		assert((std::bit_cast<intptr_t>(ptr) & 3) == 0);
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#endif
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		return *std::bit_cast<const uint32_t*>(ptr);
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	} else {
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		uint32_t result;
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		memcpy(&result, ptr, sizeof(result));
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		return result;
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	}
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}
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template<bool ALIGNED, uint8_t MASK8 = 0xFF, uint32_t SEED = 0>
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[[nodiscard]] inline uint32_t xxhash_impl(const uint8_t* p, size_t size)
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{
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	constexpr uint32_t MASK32 = MASK8 * 0x01010101U;
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	const uint8_t* const bEnd = p + size;
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	uint32_t h32;
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	if (size >= 16) [[unlikely]] {
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		const uint8_t* const limit = bEnd - 16;
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		// casts to avoid: warning C4307: '+': integral constant overflow
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		auto v1 = uint32_t(SEED + PRIME32_1 + uint64_t(PRIME32_2));
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		auto v2 = SEED + PRIME32_2;
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		auto v3 = SEED + 0;
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		auto v4 = SEED - PRIME32_1;
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		do {
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			uint32_t r1 = (read32<ALIGNED>(p +  0) & MASK32) * PRIME32_2;
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			uint32_t r2 = (read32<ALIGNED>(p +  4) & MASK32) * PRIME32_2;
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			uint32_t r3 = (read32<ALIGNED>(p +  8) & MASK32) * PRIME32_2;
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			uint32_t r4 = (read32<ALIGNED>(p + 12) & MASK32) * PRIME32_2;
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			p += 16;
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			v1 = std::rotl(v1 + r1, 13) * PRIME32_1;
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			v2 = std::rotl(v2 + r2, 13) * PRIME32_1;
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			v3 = std::rotl(v3 + r3, 13) * PRIME32_1;
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			v4 = std::rotl(v4 + r4, 13) * PRIME32_1;
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		} while (p <= limit);
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		h32 = std::rotl(v1, 1) + std::rotl(v2, 7) + std::rotl(v3, 12) + std::rotl(v4, 18);
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	} else {
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		h32  = SEED + PRIME32_5;
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	}
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	h32 += uint32_t(size);
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	while ((p + 4) <= bEnd) {
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		uint32_t r = (read32<ALIGNED>(p) & MASK32) * PRIME32_3;
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		h32  = std::rotl(h32 + r, 17) * PRIME32_4;
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		p += 4;
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	}
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	while (p < bEnd) {
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		uint32_t r = (*p & MASK8) * PRIME32_5;
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		h32 = std::rotl(h32 + r, 11) * PRIME32_1;
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		p += 1;
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	}
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	h32  = (h32 ^ (h32 >> 15)) * PRIME32_2;
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	h32  = (h32 ^ (h32 >> 13)) * PRIME32_3;
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	return  h32 ^ (h32 >> 16);
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}
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template<uint8_t MASK8> [[nodiscard]] inline uint32_t xxhash_impl(std::string_view key)
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{
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	const auto* data = std::bit_cast<const uint8_t*>(key.data());
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	auto  size = key.size();
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	if (std::bit_cast<intptr_t>(data) & 3) {
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		return xxhash_impl<false, MASK8>(data, size);
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	} else {
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		// Input is aligned, let's leverage the speed advantage
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		return xxhash_impl<true,  MASK8>(data, size);
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	}
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}
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[[nodiscard]] inline uint32_t xxhash(std::string_view key)
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{
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	return xxhash_impl<0xFF>(key);
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}
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[[nodiscard]] inline uint32_t xxhash_case(std::string_view key)
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{
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	return xxhash_impl<static_cast<uint8_t>(~('a' - 'A'))>(key);
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}
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struct XXHasher {
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	[[nodiscard]] uint32_t operator()(std::string_view key) const {
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		return xxhash(key);
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	}
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};
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struct XXHasher_IgnoreCase {
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	[[nodiscard]] uint32_t operator()(std::string_view key) const {
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		return xxhash_case(key);
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	}
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};
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#endif