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common: Port cityhash code from Citra.

nce_cpp
bunnei 8 years ago
parent
f1915d909e
commit
c30c48e052
5 changed files with 502 additions and 147 deletions
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  1. 3
      src/common/CMakeLists.txt
  2. 340
      src/common/cityhash.cpp
  3. 110
      src/common/cityhash.h
  4. 141
      src/common/hash.cpp
  5. 55
      src/common/hash.h

3
src/common/CMakeLists.txt
View File

@ -32,6 +32,8 @@ add_library(common STATIC
break_points.cpp break_points.cpp
break_points.h break_points.h
chunk_file.h chunk_file.h
cityhash.cpp
cityhash.h
code_block.h code_block.h
color.h color.h
common_funcs.h common_funcs.h
@ -39,7 +41,6 @@ add_library(common STATIC
common_types.h common_types.h
file_util.cpp file_util.cpp
file_util.h file_util.h
hash.cpp
hash.h hash.h
linear_disk_cache.h linear_disk_cache.h
logging/backend.cpp logging/backend.cpp

340
src/common/cityhash.cpp
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@ -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

110
src/common/cityhash.h
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@ -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

141
src/common/hash.cpp
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@ -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

55
src/common/hash.h
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@ -5,12 +5,12 @@
#pragma once #pragma once
#include <cstddef> #include <cstddef>
#include <cstring>
#include "common/cityhash.h"
#include "common/common_types.h" #include "common/common_types.h"
namespace Common { 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 * Computes a 64-bit hash over the specified block of data
* @param data Block of data to compute hash over * @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 * @returns 64-bit hash value that was computed over the data block
*/ */
static inline u64 ComputeHash64(const void* data, size_t len) { 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 } // namespace Common
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