322 lines
10 KiB
C++
322 lines
10 KiB
C++
// SPDX-FileCopyrightText: 2011 Google, Inc.
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// SPDX-FileContributor: Geoff Pike
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// SPDX-FileContributor: Jyrki Alakuijala
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// SPDX-License-Identifier: MIT
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// CityHash, by Geoff Pike and Jyrki Alakuijala
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//
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// This file provides CityHash64() and related functions.
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//
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// It's probably possible to create even faster hash functions by
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// writing a program that systematically explores some of the space of
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// possible hash functions, by using SIMD instructions, or by
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// compromising on hash quality.
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#include <algorithm>
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#include <cstring>
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#include <utility>
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#include "common/cityhash.h"
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#include "common/swap.h"
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// #include "config.h"
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#ifdef __GNUC__
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#define HAVE_BUILTIN_EXPECT 1
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#endif
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#ifdef COMMON_BIG_ENDIAN
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#define WORDS_BIGENDIAN 1
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#endif
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using namespace std;
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namespace Common {
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static u64 unaligned_load64(const char* p) {
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u64 result;
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std::memcpy(&result, p, sizeof(result));
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return result;
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}
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static u32 unaligned_load32(const char* p) {
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u32 result;
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std::memcpy(&result, p, sizeof(result));
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return result;
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}
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#ifdef WORDS_BIGENDIAN
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#define uint32_in_expected_order(x) (swap32(x))
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#define uint64_in_expected_order(x) (swap64(x))
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#else
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#define uint32_in_expected_order(x) (x)
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#define uint64_in_expected_order(x) (x)
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#endif
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#if !defined(LIKELY)
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#if HAVE_BUILTIN_EXPECT
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#define LIKELY(x) (__builtin_expect(!!(x), 1))
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#else
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#define LIKELY(x) (x)
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#endif
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#endif
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static u64 Fetch64(const char* p) {
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return uint64_in_expected_order(unaligned_load64(p));
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}
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static u32 Fetch32(const char* p) {
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return uint32_in_expected_order(unaligned_load32(p));
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}
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// Some primes between 2^63 and 2^64 for various uses.
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static constexpr u64 k0 = 0xc3a5c85c97cb3127ULL;
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static constexpr u64 k1 = 0xb492b66fbe98f273ULL;
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static constexpr u64 k2 = 0x9ae16a3b2f90404fULL;
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// Bitwise right rotate. Normally this will compile to a single
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// instruction, especially if the shift is a manifest constant.
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static u64 Rotate(u64 val, int shift) {
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// Avoid shifting by 64: doing so yields an undefined result.
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return shift == 0 ? val : ((val >> shift) | (val << (64 - shift)));
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}
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static u64 ShiftMix(u64 val) {
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return val ^ (val >> 47);
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}
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static u64 HashLen16(u64 u, u64 v) {
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return Hash128to64(u128{u, v});
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}
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static u64 HashLen16(u64 u, u64 v, u64 mul) {
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// Murmur-inspired hashing.
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u64 a = (u ^ v) * mul;
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a ^= (a >> 47);
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u64 b = (v ^ a) * mul;
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b ^= (b >> 47);
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b *= mul;
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return b;
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}
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static u64 HashLen0to16(const char* s, size_t len) {
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if (len >= 8) {
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u64 mul = k2 + len * 2;
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u64 a = Fetch64(s) + k2;
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u64 b = Fetch64(s + len - 8);
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u64 c = Rotate(b, 37) * mul + a;
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u64 d = (Rotate(a, 25) + b) * mul;
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return HashLen16(c, d, mul);
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}
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if (len >= 4) {
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u64 mul = k2 + len * 2;
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u64 a = Fetch32(s);
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return HashLen16(len + (a << 3), Fetch32(s + len - 4), mul);
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}
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if (len > 0) {
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u8 a = s[0];
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u8 b = s[len >> 1];
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u8 c = s[len - 1];
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u32 y = static_cast<u32>(a) + (static_cast<u32>(b) << 8);
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u32 z = static_cast<u32>(len) + (static_cast<u32>(c) << 2);
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return ShiftMix(y * k2 ^ z * k0) * k2;
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}
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return k2;
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}
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// This probably works well for 16-byte strings as well, but it may be overkill
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// in that case.
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static u64 HashLen17to32(const char* s, size_t len) {
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u64 mul = k2 + len * 2;
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u64 a = Fetch64(s) * k1;
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u64 b = Fetch64(s + 8);
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u64 c = Fetch64(s + len - 8) * mul;
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u64 d = Fetch64(s + len - 16) * k2;
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return HashLen16(Rotate(a + b, 43) + Rotate(c, 30) + d, a + Rotate(b + k2, 18) + c, mul);
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}
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// Return a 16-byte hash for 48 bytes. Quick and dirty.
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// Callers do best to use "random-looking" values for a and b.
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static pair<u64, u64> WeakHashLen32WithSeeds(u64 w, u64 x, u64 y, u64 z, u64 a, u64 b) {
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a += w;
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b = Rotate(b + a + z, 21);
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u64 c = a;
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a += x;
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a += y;
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b += Rotate(a, 44);
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return make_pair(a + z, b + c);
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}
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// Return a 16-byte hash for s[0] ... s[31], a, and b. Quick and dirty.
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static pair<u64, u64> WeakHashLen32WithSeeds(const char* s, u64 a, u64 b) {
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return WeakHashLen32WithSeeds(Fetch64(s), Fetch64(s + 8), Fetch64(s + 16), Fetch64(s + 24), a,
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b);
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}
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// Return an 8-byte hash for 33 to 64 bytes.
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static u64 HashLen33to64(const char* s, size_t len) {
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u64 mul = k2 + len * 2;
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u64 a = Fetch64(s) * k2;
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u64 b = Fetch64(s + 8);
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u64 c = Fetch64(s + len - 24);
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u64 d = Fetch64(s + len - 32);
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u64 e = Fetch64(s + 16) * k2;
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u64 f = Fetch64(s + 24) * 9;
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u64 g = Fetch64(s + len - 8);
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u64 h = Fetch64(s + len - 16) * mul;
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u64 u = Rotate(a + g, 43) + (Rotate(b, 30) + c) * 9;
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u64 v = ((a + g) ^ d) + f + 1;
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u64 w = swap64((u + v) * mul) + h;
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u64 x = Rotate(e + f, 42) + c;
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u64 y = (swap64((v + w) * mul) + g) * mul;
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u64 z = e + f + c;
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a = swap64((x + z) * mul + y) + b;
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b = ShiftMix((z + a) * mul + d + h) * mul;
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return b + x;
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}
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u64 CityHash64(const char* s, size_t len) {
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if (len <= 32) {
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if (len <= 16) {
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return HashLen0to16(s, len);
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} else {
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return HashLen17to32(s, len);
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}
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} else if (len <= 64) {
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return HashLen33to64(s, len);
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}
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// For strings over 64 bytes we hash the end first, and then as we
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// loop we keep 56 bytes of state: v, w, x, y, and z.
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u64 x = Fetch64(s + len - 40);
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u64 y = Fetch64(s + len - 16) + Fetch64(s + len - 56);
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u64 z = HashLen16(Fetch64(s + len - 48) + len, Fetch64(s + len - 24));
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pair<u64, u64> v = WeakHashLen32WithSeeds(s + len - 64, len, z);
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pair<u64, u64> w = WeakHashLen32WithSeeds(s + len - 32, y + k1, x);
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x = x * k1 + Fetch64(s);
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// Decrease len to the nearest multiple of 64, and operate on 64-byte chunks.
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len = (len - 1) & ~static_cast<size_t>(63);
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do {
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x = Rotate(x + y + v.first + Fetch64(s + 8), 37) * k1;
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y = Rotate(y + v.second + Fetch64(s + 48), 42) * k1;
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x ^= w.second;
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y += v.first + Fetch64(s + 40);
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z = Rotate(z + w.first, 33) * k1;
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v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first);
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w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + Fetch64(s + 16));
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std::swap(z, x);
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s += 64;
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len -= 64;
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} while (len != 0);
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return HashLen16(HashLen16(v.first, w.first) + ShiftMix(y) * k1 + z,
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HashLen16(v.second, w.second) + x);
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}
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u64 CityHash64WithSeed(const char* s, size_t len, u64 seed) {
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return CityHash64WithSeeds(s, len, k2, seed);
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}
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u64 CityHash64WithSeeds(const char* s, size_t len, u64 seed0, u64 seed1) {
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return HashLen16(CityHash64(s, len) - seed0, seed1);
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}
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// A subroutine for CityHash128(). Returns a decent 128-bit hash for strings
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// of any length representable in signed long. Based on City and Murmur.
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static u128 CityMurmur(const char* s, size_t len, u128 seed) {
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u64 a = seed[0];
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u64 b = seed[1];
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u64 c = 0;
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u64 d = 0;
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signed long l = static_cast<long>(len) - 16;
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if (l <= 0) { // len <= 16
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a = ShiftMix(a * k1) * k1;
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c = b * k1 + HashLen0to16(s, len);
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d = ShiftMix(a + (len >= 8 ? Fetch64(s) : c));
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} else { // len > 16
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c = HashLen16(Fetch64(s + len - 8) + k1, a);
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d = HashLen16(b + len, c + Fetch64(s + len - 16));
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a += d;
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do {
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a ^= ShiftMix(Fetch64(s) * k1) * k1;
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a *= k1;
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b ^= a;
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c ^= ShiftMix(Fetch64(s + 8) * k1) * k1;
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c *= k1;
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d ^= c;
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s += 16;
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l -= 16;
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} while (l > 0);
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}
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a = HashLen16(a, c);
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b = HashLen16(d, b);
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return u128{a ^ b, HashLen16(b, a)};
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}
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u128 CityHash128WithSeed(const char* s, size_t len, u128 seed) {
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if (len < 128) {
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return CityMurmur(s, len, seed);
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}
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// We expect len >= 128 to be the common case. Keep 56 bytes of state:
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// v, w, x, y, and z.
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pair<u64, u64> v, w;
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u64 x = seed[0];
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u64 y = seed[1];
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u64 z = len * k1;
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v.first = Rotate(y ^ k1, 49) * k1 + Fetch64(s);
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v.second = Rotate(v.first, 42) * k1 + Fetch64(s + 8);
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w.first = Rotate(y + z, 35) * k1 + x;
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w.second = Rotate(x + Fetch64(s + 88), 53) * k1;
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// This is the same inner loop as CityHash64(), manually unrolled.
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do {
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x = Rotate(x + y + v.first + Fetch64(s + 8), 37) * k1;
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y = Rotate(y + v.second + Fetch64(s + 48), 42) * k1;
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x ^= w.second;
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y += v.first + Fetch64(s + 40);
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z = Rotate(z + w.first, 33) * k1;
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v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first);
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w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + Fetch64(s + 16));
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std::swap(z, x);
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s += 64;
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x = Rotate(x + y + v.first + Fetch64(s + 8), 37) * k1;
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y = Rotate(y + v.second + Fetch64(s + 48), 42) * k1;
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x ^= w.second;
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y += v.first + Fetch64(s + 40);
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z = Rotate(z + w.first, 33) * k1;
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v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first);
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w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + Fetch64(s + 16));
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std::swap(z, x);
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s += 64;
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len -= 128;
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} while (LIKELY(len >= 128));
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x += Rotate(v.first + z, 49) * k0;
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y = y * k0 + Rotate(w.second, 37);
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z = z * k0 + Rotate(w.first, 27);
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w.first *= 9;
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v.first *= k0;
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// If 0 < len < 128, hash up to 4 chunks of 32 bytes each from the end of s.
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for (size_t tail_done = 0; tail_done < len;) {
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tail_done += 32;
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y = Rotate(x + y, 42) * k0 + v.second;
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w.first += Fetch64(s + len - tail_done + 16);
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x = x * k0 + w.first;
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z += w.second + Fetch64(s + len - tail_done);
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w.second += v.first;
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v = WeakHashLen32WithSeeds(s + len - tail_done, v.first + z, v.second);
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v.first *= k0;
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}
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// At this point our 56 bytes of state should contain more than
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// enough information for a strong 128-bit hash. We use two
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// different 56-byte-to-8-byte hashes to get a 16-byte final result.
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x = HashLen16(x, v.first);
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y = HashLen16(y + z, w.first);
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return u128{HashLen16(x + v.second, w.second) + y, HashLen16(x + w.second, y + v.second)};
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}
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u128 CityHash128(const char* s, size_t len) {
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return len >= 16 ? CityHash128WithSeed(s + 16, len - 16, u128{Fetch64(s), Fetch64(s + 8) + k0})
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: CityHash128WithSeed(s, len, u128{k0, k1});
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}
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} // namespace Common
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