// SPDX-FileCopyrightText: 2011 Google, Inc.
// SPDX-FileContributor: Geoff Pike
// SPDX-FileContributor: Jyrki Alakuijala
// SPDX-License-Identifier: MIT
// 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 <cstring>
#include <utility>
#include "common/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;
namespace Common {
static u64 unaligned_load64(const char* p) {
u64 result;
std::memcpy(&result, p, sizeof(result));
return result;
}
static u32 unaligned_load32(const char* p) {
u32 result;
std::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 u64 Fetch64(const char* p) {
return uint64_in_expected_order(unaligned_load64(p));
}
static u32 Fetch32(const char* p) {
return uint32_in_expected_order(unaligned_load32(p));
}
// Some primes between 2^63 and 2^64 for various uses.
static constexpr u64 k0 = 0xc3a5c85c97cb3127ULL;
static constexpr u64 k1 = 0xb492b66fbe98f273ULL;
static constexpr u64 k2 = 0x9ae16a3b2f90404fULL;
// Bitwise right rotate. Normally this will compile to a single
// instruction, especially if the shift is a manifest constant.
static u64 Rotate(u64 val, int shift) {
// Avoid shifting by 64: doing so yields an undefined result.
return shift == 0 ? val : ((val >> shift) | (val << (64 - shift)));
}
static u64 ShiftMix(u64 val) {
return val ^ (val >> 47);
}
static u64 HashLen16(u64 u, u64 v) {
return Hash128to64(u128{u, v});
}
static u64 HashLen16(u64 u, u64 v, u64 mul) {
// Murmur-inspired hashing.
u64 a = (u ^ v) * mul;
a ^= (a >> 47);
u64 b = (v ^ a) * mul;
b ^= (b >> 47);
b *= mul;
return b;
}
static u64 HashLen0to16(const char* s, size_t len) {
if (len >= 8) {
u64 mul = k2 + len * 2;
u64 a = Fetch64(s) + k2;
u64 b = Fetch64(s + len - 8);
u64 c = Rotate(b, 37) * mul + a;
u64 d = (Rotate(a, 25) + b) * mul;
return HashLen16(c, d, mul);
}
if (len >= 4) {
u64 mul = k2 + len * 2;
u64 a = Fetch32(s);
return HashLen16(len + (a << 3), Fetch32(s + len - 4), mul);
}
if (len > 0) {
u8 a = s[0];
u8 b = s[len >> 1];
u8 c = s[len - 1];
u32 y = static_cast<u32>(a) + (static_cast<u32>(b) << 8);
u32 z = static_cast<u32>(len) + (static_cast<u32>(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 u64 HashLen17to32(const char* s, size_t len) {
u64 mul = k2 + len * 2;
u64 a = Fetch64(s) * k1;
u64 b = Fetch64(s + 8);
u64 c = Fetch64(s + len - 8) * mul;
u64 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<u64, u64> WeakHashLen32WithSeeds(u64 w, u64 x, u64 y, u64 z, u64 a, u64 b) {
a += w;
b = Rotate(b + a + z, 21);
u64 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<u64, u64> WeakHashLen32WithSeeds(const char* s, u64 a, u64 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 u64 HashLen33to64(const char* s, size_t len) {
u64 mul = k2 + len * 2;
u64 a = Fetch64(s) * k2;
u64 b = Fetch64(s + 8);
u64 c = Fetch64(s + len - 24);
u64 d = Fetch64(s + len - 32);
u64 e = Fetch64(s + 16) * k2;
u64 f = Fetch64(s + 24) * 9;
u64 g = Fetch64(s + len - 8);
u64 h = Fetch64(s + len - 16) * mul;
u64 u = Rotate(a + g, 43) + (Rotate(b, 30) + c) * 9;
u64 v = ((a + g) ^ d) + f + 1;
u64 w = swap64((u + v) * mul) + h;
u64 x = Rotate(e + f, 42) + c;
u64 y = (swap64((v + w) * mul) + g) * mul;
u64 z = e + f + c;
a = swap64((x + z) * mul + y) + b;
b = ShiftMix((z + a) * mul + d + h) * mul;
return b + x;
}
u64 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.
u64 x = Fetch64(s + len - 40);
u64 y = Fetch64(s + len - 16) + Fetch64(s + len - 56);
u64 z = HashLen16(Fetch64(s + len - 48) + len, Fetch64(s + len - 24));
pair<u64, u64> v = WeakHashLen32WithSeeds(s + len - 64, len, z);
pair<u64, u64> 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);
}
u64 CityHash64WithSeed(const char* s, size_t len, u64 seed) {
return CityHash64WithSeeds(s, len, k2, seed);
}
u64 CityHash64WithSeeds(const char* s, size_t len, u64 seed0, u64 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 u128 CityMurmur(const char* s, size_t len, u128 seed) {
u64 a = seed[0];
u64 b = seed[1];
u64 c = 0;
u64 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 u128{a ^ b, HashLen16(b, a)};
}
u128 CityHash128WithSeed(const char* s, size_t len, u128 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<u64, u64> v, w;
u64 x = seed[0];
u64 y = seed[1];
u64 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 u128{HashLen16(x + v.second, w.second) + y, HashLen16(x + w.second, y + v.second)};
}
u128 CityHash128(const char* s, size_t len) {
return len >= 16 ? CityHash128WithSeed(s + 16, len - 16, u128{Fetch64(s), Fetch64(s + 8) + k0})
: CityHash128WithSeed(s, len, u128{k0, k1});
}
} // namespace Common
