diff options
Diffstat (limited to 'src/common')
| -rw-r--r-- | src/common/CMakeLists.txt | 3 | ||||
| -rw-r--r-- | src/common/cityhash.cpp | 340 | ||||
| -rw-r--r-- | src/common/cityhash.h | 110 | ||||
| -rw-r--r-- | src/common/hash.cpp | 141 | ||||
| -rw-r--r-- | src/common/hash.h | 55 |
5 files changed, 502 insertions, 147 deletions
diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt index 2ba1da195..d6eb9055b 100644 --- a/src/common/CMakeLists.txt +++ b/src/common/CMakeLists.txt @@ -32,6 +32,8 @@ add_library(common STATIC break_points.cpp break_points.h chunk_file.h + cityhash.cpp + cityhash.h code_block.h color.h common_funcs.h @@ -39,7 +41,6 @@ add_library(common STATIC common_types.h file_util.cpp file_util.h - hash.cpp hash.h linear_disk_cache.h logging/backend.cpp diff --git a/src/common/cityhash.cpp b/src/common/cityhash.cpp new file mode 100644 index 000000000..de31ffbd8 --- /dev/null +++ b/src/common/cityhash.cpp @@ -0,0 +1,340 @@ +// Copyright (c) 2011 Google, Inc. +// +// Permission is hereby granted, free of charge, to any person obtaining a copy +// of this software and associated documentation files (the "Software"), to deal +// in the Software without restriction, including without limitation the rights +// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +// copies of the Software, and to permit persons to whom the Software is +// furnished to do so, subject to the following conditions: +// +// The above copyright notice and this permission notice shall be included in +// all copies or substantial portions of the Software. +// +// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN +// THE SOFTWARE. +// +// CityHash, by Geoff Pike and Jyrki Alakuijala +// +// This file provides CityHash64() and related functions. +// +// It's probably possible to create even faster hash functions by +// writing a program that systematically explores some of the space of +// possible hash functions, by using SIMD instructions, or by +// compromising on hash quality. + +#include <algorithm> +#include <string.h> // for memcpy and memset +#include "cityhash.h" +#include "common/swap.h" + +// #include "config.h" +#ifdef __GNUC__ +#define HAVE_BUILTIN_EXPECT 1 +#endif +#ifdef COMMON_BIG_ENDIAN +#define WORDS_BIGENDIAN 1 +#endif + +using namespace std; + +typedef uint8_t uint8; +typedef uint32_t uint32; +typedef uint64_t uint64; + +namespace Common { + +static uint64 UNALIGNED_LOAD64(const char* p) { + uint64 result; + memcpy(&result, p, sizeof(result)); + return result; +} + +static uint32 UNALIGNED_LOAD32(const char* p) { + uint32 result; + memcpy(&result, p, sizeof(result)); + return result; +} + +#ifdef WORDS_BIGENDIAN +#define uint32_in_expected_order(x) (swap32(x)) +#define uint64_in_expected_order(x) (swap64(x)) +#else +#define uint32_in_expected_order(x) (x) +#define uint64_in_expected_order(x) (x) +#endif + +#if !defined(LIKELY) +#if HAVE_BUILTIN_EXPECT +#define LIKELY(x) (__builtin_expect(!!(x), 1)) +#else +#define LIKELY(x) (x) +#endif +#endif + +static uint64 Fetch64(const char* p) { + return uint64_in_expected_order(UNALIGNED_LOAD64(p)); +} + +static uint32 Fetch32(const char* p) { + return uint32_in_expected_order(UNALIGNED_LOAD32(p)); +} + +// Some primes between 2^63 and 2^64 for various uses. +static const uint64 k0 = 0xc3a5c85c97cb3127ULL; +static const uint64 k1 = 0xb492b66fbe98f273ULL; +static const uint64 k2 = 0x9ae16a3b2f90404fULL; + +// Bitwise right rotate. Normally this will compile to a single +// instruction, especially if the shift is a manifest constant. +static uint64 Rotate(uint64 val, int shift) { + // Avoid shifting by 64: doing so yields an undefined result. + return shift == 0 ? val : ((val >> shift) | (val << (64 - shift))); +} + +static uint64 ShiftMix(uint64 val) { + return val ^ (val >> 47); +} + +static uint64 HashLen16(uint64 u, uint64 v) { + return Hash128to64(uint128(u, v)); +} + +static uint64 HashLen16(uint64 u, uint64 v, uint64 mul) { + // Murmur-inspired hashing. + uint64 a = (u ^ v) * mul; + a ^= (a >> 47); + uint64 b = (v ^ a) * mul; + b ^= (b >> 47); + b *= mul; + return b; +} + +static uint64 HashLen0to16(const char* s, size_t len) { + if (len >= 8) { + uint64 mul = k2 + len * 2; + uint64 a = Fetch64(s) + k2; + uint64 b = Fetch64(s + len - 8); + uint64 c = Rotate(b, 37) * mul + a; + uint64 d = (Rotate(a, 25) + b) * mul; + return HashLen16(c, d, mul); + } + if (len >= 4) { + uint64 mul = k2 + len * 2; + uint64 a = Fetch32(s); + return HashLen16(len + (a << 3), Fetch32(s + len - 4), mul); + } + if (len > 0) { + uint8 a = s[0]; + uint8 b = s[len >> 1]; + uint8 c = s[len - 1]; + uint32 y = static_cast<uint32>(a) + (static_cast<uint32>(b) << 8); + uint32 z = static_cast<uint32>(len) + (static_cast<uint32>(c) << 2); + return ShiftMix(y * k2 ^ z * k0) * k2; + } + return k2; +} + +// This probably works well for 16-byte strings as well, but it may be overkill +// in that case. +static uint64 HashLen17to32(const char* s, size_t len) { + uint64 mul = k2 + len * 2; + uint64 a = Fetch64(s) * k1; + uint64 b = Fetch64(s + 8); + uint64 c = Fetch64(s + len - 8) * mul; + uint64 d = Fetch64(s + len - 16) * k2; + return HashLen16(Rotate(a + b, 43) + Rotate(c, 30) + d, a + Rotate(b + k2, 18) + c, mul); +} + +// Return a 16-byte hash for 48 bytes. Quick and dirty. +// Callers do best to use "random-looking" values for a and b. +static pair<uint64, uint64> WeakHashLen32WithSeeds(uint64 w, uint64 x, uint64 y, uint64 z, uint64 a, + uint64 b) { + a += w; + b = Rotate(b + a + z, 21); + uint64 c = a; + a += x; + a += y; + b += Rotate(a, 44); + return make_pair(a + z, b + c); +} + +// Return a 16-byte hash for s[0] ... s[31], a, and b. Quick and dirty. +static pair<uint64, uint64> WeakHashLen32WithSeeds(const char* s, uint64 a, uint64 b) { + return WeakHashLen32WithSeeds(Fetch64(s), Fetch64(s + 8), Fetch64(s + 16), Fetch64(s + 24), a, + b); +} + +// Return an 8-byte hash for 33 to 64 bytes. +static uint64 HashLen33to64(const char* s, size_t len) { + uint64 mul = k2 + len * 2; + uint64 a = Fetch64(s) * k2; + uint64 b = Fetch64(s + 8); + uint64 c = Fetch64(s + len - 24); + uint64 d = Fetch64(s + len - 32); + uint64 e = Fetch64(s + 16) * k2; + uint64 f = Fetch64(s + 24) * 9; + uint64 g = Fetch64(s + len - 8); + uint64 h = Fetch64(s + len - 16) * mul; + uint64 u = Rotate(a + g, 43) + (Rotate(b, 30) + c) * 9; + uint64 v = ((a + g) ^ d) + f + 1; + uint64 w = swap64((u + v) * mul) + h; + uint64 x = Rotate(e + f, 42) + c; + uint64 y = (swap64((v + w) * mul) + g) * mul; + uint64 z = e + f + c; + a = swap64((x + z) * mul + y) + b; + b = ShiftMix((z + a) * mul + d + h) * mul; + return b + x; +} + +uint64 CityHash64(const char* s, size_t len) { + if (len <= 32) { + if (len <= 16) { + return HashLen0to16(s, len); + } else { + return HashLen17to32(s, len); + } + } else if (len <= 64) { + return HashLen33to64(s, len); + } + + // For strings over 64 bytes we hash the end first, and then as we + // loop we keep 56 bytes of state: v, w, x, y, and z. + uint64 x = Fetch64(s + len - 40); + uint64 y = Fetch64(s + len - 16) + Fetch64(s + len - 56); + uint64 z = HashLen16(Fetch64(s + len - 48) + len, Fetch64(s + len - 24)); + pair<uint64, uint64> v = WeakHashLen32WithSeeds(s + len - 64, len, z); + pair<uint64, uint64> w = WeakHashLen32WithSeeds(s + len - 32, y + k1, x); + x = x * k1 + Fetch64(s); + + // Decrease len to the nearest multiple of 64, and operate on 64-byte chunks. + len = (len - 1) & ~static_cast<size_t>(63); + do { + x = Rotate(x + y + v.first + Fetch64(s + 8), 37) * k1; + y = Rotate(y + v.second + Fetch64(s + 48), 42) * k1; + x ^= w.second; + y += v.first + Fetch64(s + 40); + z = Rotate(z + w.first, 33) * k1; + v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first); + w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + Fetch64(s + 16)); + std::swap(z, x); + s += 64; + len -= 64; + } while (len != 0); + return HashLen16(HashLen16(v.first, w.first) + ShiftMix(y) * k1 + z, + HashLen16(v.second, w.second) + x); +} + +uint64 CityHash64WithSeed(const char* s, size_t len, uint64 seed) { + return CityHash64WithSeeds(s, len, k2, seed); +} + +uint64 CityHash64WithSeeds(const char* s, size_t len, uint64 seed0, uint64 seed1) { + return HashLen16(CityHash64(s, len) - seed0, seed1); +} + +// A subroutine for CityHash128(). Returns a decent 128-bit hash for strings +// of any length representable in signed long. Based on City and Murmur. +static uint128 CityMurmur(const char* s, size_t len, uint128 seed) { + uint64 a = Uint128Low64(seed); + uint64 b = Uint128High64(seed); + uint64 c = 0; + uint64 d = 0; + signed long l = static_cast<long>(len) - 16; + if (l <= 0) { // len <= 16 + a = ShiftMix(a * k1) * k1; + c = b * k1 + HashLen0to16(s, len); + d = ShiftMix(a + (len >= 8 ? Fetch64(s) : c)); + } else { // len > 16 + c = HashLen16(Fetch64(s + len - 8) + k1, a); + d = HashLen16(b + len, c + Fetch64(s + len - 16)); + a += d; + do { + a ^= ShiftMix(Fetch64(s) * k1) * k1; + a *= k1; + b ^= a; + c ^= ShiftMix(Fetch64(s + 8) * k1) * k1; + c *= k1; + d ^= c; + s += 16; + l -= 16; + } while (l > 0); + } + a = HashLen16(a, c); + b = HashLen16(d, b); + return uint128(a ^ b, HashLen16(b, a)); +} + +uint128 CityHash128WithSeed(const char* s, size_t len, uint128 seed) { + if (len < 128) { + return CityMurmur(s, len, seed); + } + + // We expect len >= 128 to be the common case. Keep 56 bytes of state: + // v, w, x, y, and z. + pair<uint64, uint64> v, w; + uint64 x = Uint128Low64(seed); + uint64 y = Uint128High64(seed); + uint64 z = len * k1; + v.first = Rotate(y ^ k1, 49) * k1 + Fetch64(s); + v.second = Rotate(v.first, 42) * k1 + Fetch64(s + 8); + w.first = Rotate(y + z, 35) * k1 + x; + w.second = Rotate(x + Fetch64(s + 88), 53) * k1; + + // This is the same inner loop as CityHash64(), manually unrolled. + do { + x = Rotate(x + y + v.first + Fetch64(s + 8), 37) * k1; + y = Rotate(y + v.second + Fetch64(s + 48), 42) * k1; + x ^= w.second; + y += v.first + Fetch64(s + 40); + z = Rotate(z + w.first, 33) * k1; + v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first); + w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + Fetch64(s + 16)); + std::swap(z, x); + s += 64; + x = Rotate(x + y + v.first + Fetch64(s + 8), 37) * k1; + y = Rotate(y + v.second + Fetch64(s + 48), 42) * k1; + x ^= w.second; + y += v.first + Fetch64(s + 40); + z = Rotate(z + w.first, 33) * k1; + v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first); + w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + Fetch64(s + 16)); + std::swap(z, x); + s += 64; + len -= 128; + } while (LIKELY(len >= 128)); + x += Rotate(v.first + z, 49) * k0; + y = y * k0 + Rotate(w.second, 37); + z = z * k0 + Rotate(w.first, 27); + w.first *= 9; + v.first *= k0; + // If 0 < len < 128, hash up to 4 chunks of 32 bytes each from the end of s. + for (size_t tail_done = 0; tail_done < len;) { + tail_done += 32; + y = Rotate(x + y, 42) * k0 + v.second; + w.first += Fetch64(s + len - tail_done + 16); + x = x * k0 + w.first; + z += w.second + Fetch64(s + len - tail_done); + w.second += v.first; + v = WeakHashLen32WithSeeds(s + len - tail_done, v.first + z, v.second); + v.first *= k0; + } + // At this point our 56 bytes of state should contain more than + // enough information for a strong 128-bit hash. We use two + // different 56-byte-to-8-byte hashes to get a 16-byte final result. + x = HashLen16(x, v.first); + y = HashLen16(y + z, w.first); + return uint128(HashLen16(x + v.second, w.second) + y, HashLen16(x + w.second, y + v.second)); +} + +uint128 CityHash128(const char* s, size_t len) { + return len >= 16 + ? CityHash128WithSeed(s + 16, len - 16, uint128(Fetch64(s), Fetch64(s + 8) + k0)) + : CityHash128WithSeed(s, len, uint128(k0, k1)); +} + +} // namespace Common diff --git a/src/common/cityhash.h b/src/common/cityhash.h new file mode 100644 index 000000000..bcebdb150 --- /dev/null +++ b/src/common/cityhash.h @@ -0,0 +1,110 @@ +// Copyright (c) 2011 Google, Inc. +// +// Permission is hereby granted, free of charge, to any person obtaining a copy +// of this software and associated documentation files (the "Software"), to deal +// in the Software without restriction, including without limitation the rights +// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +// copies of the Software, and to permit persons to whom the Software is +// furnished to do so, subject to the following conditions: +// +// The above copyright notice and this permission notice shall be included in +// all copies or substantial portions of the Software. +// +// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN +// THE SOFTWARE. +// +// 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 <utility> +#include <stdint.h> +#include <stdlib.h> // for size_t. + +namespace Common { + +typedef std::pair<uint64_t, uint64_t> uint128; + +inline uint64_t Uint128Low64(const uint128& x) { + return x.first; +} +inline uint64_t Uint128High64(const uint128& x) { + return x.second; +} + +// Hash function for a byte array. +uint64_t 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. +uint64_t CityHash64WithSeed(const char* buf, size_t len, uint64_t seed); + +// Hash function for a byte array. For convenience, two seeds are also +// hashed into the result. +uint64_t CityHash64WithSeeds(const char* buf, size_t len, uint64_t seed0, uint64_t seed1); + +// Hash function for a byte array. +uint128 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. +uint128 CityHash128WithSeed(const char* s, size_t len, uint128 seed); + +// Hash 128 input bits down to 64 bits of output. +// This is intended to be a reasonably good hash function. +inline uint64_t Hash128to64(const uint128& x) { + // Murmur-inspired hashing. + const uint64_t kMul = 0x9ddfea08eb382d69ULL; + uint64_t a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul; + a ^= (a >> 47); + uint64_t b = (Uint128High64(x) ^ a) * kMul; + b ^= (b >> 47); + b *= kMul; + return b; +} + +} // namespace Common diff --git a/src/common/hash.cpp b/src/common/hash.cpp deleted file mode 100644 index a02e9e5b9..000000000 --- a/src/common/hash.cpp +++ /dev/null @@ -1,141 +0,0 @@ -// Copyright 2015 Citra Emulator Project -// Licensed under GPLv2 or any later version -// Refer to the license.txt file included. - -#if defined(_MSC_VER) -#include <stdlib.h> -#endif -#include "common/common_funcs.h" -#include "common/common_types.h" -#include "common/hash.h" - -namespace Common { - -// MurmurHash3 was written by Austin Appleby, and is placed in the public -// domain. The author hereby disclaims copyright to this source code. - -// Block read - if your platform needs to do endian-swapping or can only handle aligned reads, do -// the conversion here -static FORCE_INLINE u64 getblock64(const u64* p, size_t i) { - return p[i]; -} - -// Finalization mix - force all bits of a hash block to avalanche -static FORCE_INLINE u64 fmix64(u64 k) { - k ^= k >> 33; - k *= 0xff51afd7ed558ccdllu; - k ^= k >> 33; - k *= 0xc4ceb9fe1a85ec53llu; - k ^= k >> 33; - - return k; -} - -// This is the 128-bit variant of the MurmurHash3 hash function that is targeted for 64-bit -// platforms (MurmurHash3_x64_128). It was taken from: -// https://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp -void MurmurHash3_128(const void* key, size_t len, u32 seed, void* out) { - const u8* data = (const u8*)key; - const size_t nblocks = len / 16; - - u64 h1 = seed; - u64 h2 = seed; - - const u64 c1 = 0x87c37b91114253d5llu; - const u64 c2 = 0x4cf5ad432745937fllu; - - // Body - - const u64* blocks = (const u64*)(data); - - for (size_t i = 0; i < nblocks; i++) { - u64 k1 = getblock64(blocks, i * 2 + 0); - u64 k2 = getblock64(blocks, i * 2 + 1); - - k1 *= c1; - k1 = _rotl64(k1, 31); - k1 *= c2; - h1 ^= k1; - - h1 = _rotl64(h1, 27); - h1 += h2; - h1 = h1 * 5 + 0x52dce729; - - k2 *= c2; - k2 = _rotl64(k2, 33); - k2 *= c1; - h2 ^= k2; - - h2 = _rotl64(h2, 31); - h2 += h1; - h2 = h2 * 5 + 0x38495ab5; - } - - // Tail - - const u8* tail = (const u8*)(data + nblocks * 16); - - u64 k1 = 0; - u64 k2 = 0; - - switch (len & 15) { - case 15: - k2 ^= ((u64)tail[14]) << 48; - case 14: - k2 ^= ((u64)tail[13]) << 40; - case 13: - k2 ^= ((u64)tail[12]) << 32; - case 12: - k2 ^= ((u64)tail[11]) << 24; - case 11: - k2 ^= ((u64)tail[10]) << 16; - case 10: - k2 ^= ((u64)tail[9]) << 8; - case 9: - k2 ^= ((u64)tail[8]) << 0; - k2 *= c2; - k2 = _rotl64(k2, 33); - k2 *= c1; - h2 ^= k2; - - case 8: - k1 ^= ((u64)tail[7]) << 56; - case 7: - k1 ^= ((u64)tail[6]) << 48; - case 6: - k1 ^= ((u64)tail[5]) << 40; - case 5: - k1 ^= ((u64)tail[4]) << 32; - case 4: - k1 ^= ((u64)tail[3]) << 24; - case 3: - k1 ^= ((u64)tail[2]) << 16; - case 2: - k1 ^= ((u64)tail[1]) << 8; - case 1: - k1 ^= ((u64)tail[0]) << 0; - k1 *= c1; - k1 = _rotl64(k1, 31); - k1 *= c2; - h1 ^= k1; - }; - - // Finalization - - h1 ^= len; - h2 ^= len; - - h1 += h2; - h2 += h1; - - h1 = fmix64(h1); - h2 = fmix64(h2); - - h1 += h2; - h2 += h1; - - ((u64*)out)[0] = h1; - ((u64*)out)[1] = h2; -} - -} // namespace Common diff --git a/src/common/hash.h b/src/common/hash.h index ee2560dad..73c326980 100644 --- a/src/common/hash.h +++ b/src/common/hash.h @@ -5,12 +5,12 @@ #pragma once #include <cstddef> +#include <cstring> +#include "common/cityhash.h" #include "common/common_types.h" namespace Common { -void MurmurHash3_128(const void* key, size_t len, u32 seed, void* out); - /** * Computes a 64-bit hash over the specified block of data * @param data Block of data to compute hash over @@ -18,9 +18,54 @@ void MurmurHash3_128(const void* key, size_t len, u32 seed, void* out); * @returns 64-bit hash value that was computed over the data block */ static inline u64 ComputeHash64(const void* data, size_t len) { - u64 res[2]; - MurmurHash3_128(data, len, 0, res); - return res[0]; + return CityHash64(static_cast<const char*>(data), len); +} + +/** + * Computes a 64-bit hash of a struct. In addition to being trivially copyable, it is also critical + * that either the struct includes no padding, or that any padding is initialized to a known value + * by memsetting the struct to 0 before filling it in. + */ +template <typename T> +static inline u64 ComputeStructHash64(const T& data) { + static_assert(std::is_trivially_copyable<T>(), + "Type passed to ComputeStructHash64 must be trivially copyable"); + return ComputeHash64(&data, sizeof(data)); } +/// A helper template that ensures the padding in a struct is initialized by memsetting to 0. +template <typename T> +struct HashableStruct { + // In addition to being trivially copyable, T must also have a trivial default constructor, + // because any member initialization would be overridden by memset + static_assert(std::is_trivial<T>(), "Type passed to HashableStruct must be trivial"); + /* + * We use a union because "implicitly-defined copy/move constructor for a union X copies the + * object representation of X." and "implicitly-defined copy assignment operator for a union X + * copies the object representation (3.9) of X." = Bytewise copy instead of memberwise copy. + * This is important because the padding bytes are included in the hash and comparison between + * objects. + */ + union { + T state; + }; + + HashableStruct() { + // Memset structure to zero padding bits, so that they will be deterministic when hashing + std::memset(&state, 0, sizeof(T)); + } + + bool operator==(const HashableStruct<T>& o) const { + return std::memcmp(&state, &o.state, sizeof(T)) == 0; + }; + + bool operator!=(const HashableStruct<T>& o) const { + return !(*this == o); + }; + + size_t Hash() const { + return Common::ComputeStructHash64(state); + } +}; + } // namespace Common |