mirror of
https://github.com/yuzu-mirror/yuzu.git
synced 2024-11-10 05:19:57 +00:00
86 lines
3.4 KiB
C++
86 lines
3.4 KiB
C++
// SPDX-FileCopyrightText: 2011 Google, Inc.
|
|
// SPDX-FileContributor: Geoff Pike
|
|
// SPDX-FileContributor: Jyrki Alakuijala
|
|
// SPDX-License-Identifier: MIT
|
|
|
|
// CityHash, by Geoff Pike and Jyrki Alakuijala
|
|
//
|
|
// http://code.google.com/p/cityhash/
|
|
//
|
|
// This file provides a few functions for hashing strings. All of them are
|
|
// high-quality functions in the sense that they pass standard tests such
|
|
// as Austin Appleby's SMHasher. They are also fast.
|
|
//
|
|
// For 64-bit x86 code, on short strings, we don't know of anything faster than
|
|
// CityHash64 that is of comparable quality. We believe our nearest competitor
|
|
// is Murmur3. For 64-bit x86 code, CityHash64 is an excellent choice for hash
|
|
// tables and most other hashing (excluding cryptography).
|
|
//
|
|
// For 64-bit x86 code, on long strings, the picture is more complicated.
|
|
// On many recent Intel CPUs, such as Nehalem, Westmere, Sandy Bridge, etc.,
|
|
// CityHashCrc128 appears to be faster than all competitors of comparable
|
|
// quality. CityHash128 is also good but not quite as fast. We believe our
|
|
// nearest competitor is Bob Jenkins' Spooky. We don't have great data for
|
|
// other 64-bit CPUs, but for long strings we know that Spooky is slightly
|
|
// faster than CityHash on some relatively recent AMD x86-64 CPUs, for example.
|
|
// Note that CityHashCrc128 is declared in citycrc.h.
|
|
//
|
|
// For 32-bit x86 code, we don't know of anything faster than CityHash32 that
|
|
// is of comparable quality. We believe our nearest competitor is Murmur3A.
|
|
// (On 64-bit CPUs, it is typically faster to use the other CityHash variants.)
|
|
//
|
|
// Functions in the CityHash family are not suitable for cryptography.
|
|
//
|
|
// Please see CityHash's README file for more details on our performance
|
|
// measurements and so on.
|
|
//
|
|
// WARNING: This code has been only lightly tested on big-endian platforms!
|
|
// It is known to work well on little-endian platforms that have a small penalty
|
|
// for unaligned reads, such as current Intel and AMD moderate-to-high-end CPUs.
|
|
// It should work on all 32-bit and 64-bit platforms that allow unaligned reads;
|
|
// bug reports are welcome.
|
|
//
|
|
// By the way, for some hash functions, given strings a and b, the hash
|
|
// of a+b is easily derived from the hashes of a and b. This property
|
|
// doesn't hold for any hash functions in this file.
|
|
|
|
#pragma once
|
|
|
|
#include <cstddef>
|
|
#include "common/common_types.h"
|
|
|
|
namespace Common {
|
|
|
|
// Hash function for a byte array.
|
|
[[nodiscard]] u64 CityHash64(const char* buf, size_t len);
|
|
|
|
// Hash function for a byte array. For convenience, a 64-bit seed is also
|
|
// hashed into the result.
|
|
[[nodiscard]] u64 CityHash64WithSeed(const char* buf, size_t len, u64 seed);
|
|
|
|
// Hash function for a byte array. For convenience, two seeds are also
|
|
// hashed into the result.
|
|
[[nodiscard]] u64 CityHash64WithSeeds(const char* buf, size_t len, u64 seed0, u64 seed1);
|
|
|
|
// Hash function for a byte array.
|
|
[[nodiscard]] u128 CityHash128(const char* s, size_t len);
|
|
|
|
// Hash function for a byte array. For convenience, a 128-bit seed is also
|
|
// hashed into the result.
|
|
[[nodiscard]] u128 CityHash128WithSeed(const char* s, size_t len, u128 seed);
|
|
|
|
// Hash 128 input bits down to 64 bits of output.
|
|
// This is intended to be a reasonably good hash function.
|
|
[[nodiscard]] inline u64 Hash128to64(const u128& x) {
|
|
// Murmur-inspired hashing.
|
|
const u64 mul = 0x9ddfea08eb382d69ULL;
|
|
u64 a = (x[0] ^ x[1]) * mul;
|
|
a ^= (a >> 47);
|
|
u64 b = (x[1] ^ a) * mul;
|
|
b ^= (b >> 47);
|
|
b *= mul;
|
|
return b;
|
|
}
|
|
|
|
} // namespace Common
|