hash.h File Reference

#include <concepts>
#include <cstddef>
#include <cstdint>

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Namespaces
namespace	fe

Functions
Bit Mixers
These finalizers scramble a single word. They are bijective, i.e., they don't introduce any collisions on their own - they merely spread the input bits.
constexpr uint32_t	fe::murmur3 (uint32_t h) noexcept
	MurmurHash3's 32-bit finalizer fmix32.
constexpr uint64_t	fe::splitmix64 (uint64_t h) noexcept
	SplitMix64's 64-bit finalizer.
constexpr size_t	fe::hash (size_t h) noexcept
	Mixes h with murmur3 or splitmix64 - whichever matches sizeof(size_t).

FNV-1 Hash
See Wikipedia. Use hash_begin to seed a hash chain and hash_combine to fold in one value after another: auto h = fe::hash_begin(x); for (auto elem : elems) h = fe::hash_combine(h, elem); Note These hashes are not stable: they differ between 32- and 64-bit builds and may change between fe releases. Never serialize them and never rely on the iteration order they induce.
constexpr size_t	fe::fnv1_offset = sizeof(size_t) == 4 ? size_t(UINT32_C(2166136261)) : size_t(UINT64_C(14695981039346656037))
	FNV-1 magic numbers for sizeof(size_t).
constexpr size_t	fe::fnv1_prime = sizeof(size_t) == 4 ? size_t(UINT32_C( 16777619)) : size_t(UINT64_C( 1099511628211))
constexpr size_t	fe::hash_begin () noexcept
	Seeds a hash chain with the FNV-1 offset basis.
template<std::integral T>
constexpr size_t	fe::hash_combine (size_t seed, T v) noexcept
	Mixes v into seed word-wise, reusing the FNV-1 prime as multiplier.
template<std::integral T>
constexpr size_t	fe::hash_begin (T v) noexcept
	Shorthand for hash_combine(hash_begin(), v).