143 lines
3.8 KiB
C++
143 lines
3.8 KiB
C++
// Copyright 2025 Steven Le Rouzic
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//
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// SPDX-License-Identifier: BSD-3-Clause
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#pragma once
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#include "asl/base/integers.hpp"
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#include "asl/base/meta.hpp"
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#include "asl/types/span.hpp"
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#include "asl/base/utility.hpp"
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namespace asl::city_hash
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{
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// Hash function for a byte array.
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uint64_t CityHash64(const char *s, size_t len);
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// Hash function for a byte array. For convenience, a 64-bit seed is also
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// hashed into the result.
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uint64_t CityHash64WithSeed(const char *s, size_t len, uint64_t seed);
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// Hash function for a byte array. For convenience, two seeds are also
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// hashed into the result.
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uint64_t CityHash64WithSeeds(const char *s, size_t len,
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uint64_t seed0, uint64_t seed1);
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// Hash function for a byte array.
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uint128_t CityHash128(const char *s, size_t len);
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// Hash function for a byte array. For convenience, a 128-bit seed is also
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// hashed into the result.
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uint128_t CityHash128WithSeed(const char *s, size_t len, uint128_t seed);
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// Hash function for a byte array. Most useful in 32-bit binaries.
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uint32_t CityHash32(const char *s, size_t len);
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// Hash 128 input bits down to 64 bits of output.
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// This is intended to be a reasonably good hash function.
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constexpr uint64_t Hash128to64(uint64_t high, uint64_t low)
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{
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// Murmur-inspired hashing.
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const uint64_t kMul = 0x9ddfea08eb382d69ULL;
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uint64_t a = (low ^ high) * kMul;
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a ^= (a >> 47);
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uint64_t b = (high ^ a) * kMul;
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b ^= (b >> 47);
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b *= kMul;
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return b;
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}
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// Hash 128 input bits down to 64 bits of output.
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// This is intended to be a reasonably good hash function.
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constexpr uint64_t Hash128to64(const uint128_t& x)
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{
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return Hash128to64(x.high, x.low);
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}
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} // namespace asl::city_hash
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namespace asl
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{
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template<typename T, typename H>
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concept hashable_generic = requires(const T& value, H h)
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{
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{ AslHashValue(h, value) } -> same_as<H>;
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};
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struct HashState
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{
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uint128_t state{};
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constexpr HashState() = default;
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explicit constexpr HashState(uint128_t s) : state{s} {}
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template<typename T>
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static HashState combine_contiguous(HashState h, span<const T> s)
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{
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if constexpr (uniquely_represented<T>)
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{
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auto bytes = as_bytes(s);
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auto hashed = city_hash::CityHash128WithSeed(
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reinterpret_cast<const char*>(bytes.data()), // NOLINT(*-reinterpret-cast)
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static_cast<size_t>(bytes.size()),
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h.state);
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return HashState{hashed};
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}
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else
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{
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for (const auto& value: s)
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{
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h = AslHashValue(std::move(h), value);
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}
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return h;
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}
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}
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static constexpr HashState combine(HashState h)
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{
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return h;
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}
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template<hashable_generic<HashState> Arg, hashable_generic<HashState>... Remaining>
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static constexpr HashState combine(HashState h, const Arg& arg, const Remaining&... remaining)
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{
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return combine(AslHashValue(std::move(h), arg), remaining...);
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}
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};
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template<typename T>
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concept hashable = hashable_generic<T, HashState>;
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template<typename H, uniquely_represented T>
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constexpr H AslHashValue(H h, const T& value)
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{
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return H::combine_contiguous(std::move(h), span<const T>{&value, 1});
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}
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template<typename H>
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constexpr H AslHashValue(H h, bool value)
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{
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return AslHashValue(std::move(h), value ? 1 : 0);
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}
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template<typename H, typename T>
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constexpr void AslHashValue(H h, T*); // Don't hash pointers
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template<typename H, hashable T>
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constexpr H AslHashValue(H h, const span<T>& s)
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{
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return H::combine_contiguous(std::move(h), span<const T>{s.data(), s.size()});
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}
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template<hashable T>
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constexpr uint64_t hash_value(const T& value)
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{
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auto result = AslHashValue(HashState{}, value).state;
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return city_hash::Hash128to64(result);
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}
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} // namespace asl
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