350 lines
11 KiB
C++
350 lines
11 KiB
C++
// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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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 "absl/hash/internal/city.h"
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#include <string.h> // for memcpy and memset
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#include <algorithm>
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#include "absl/base/config.h"
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#include "absl/base/internal/endian.h"
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#include "absl/base/internal/unaligned_access.h"
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#include "absl/base/optimization.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace hash_internal {
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#ifdef ABSL_IS_BIG_ENDIAN
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#define uint32_in_expected_order(x) (absl::gbswap_32(x))
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#define uint64_in_expected_order(x) (absl::gbswap_64(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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static uint64_t Fetch64(const char *p) {
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return uint64_in_expected_order(ABSL_INTERNAL_UNALIGNED_LOAD64(p));
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}
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static uint32_t Fetch32(const char *p) {
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return uint32_in_expected_order(ABSL_INTERNAL_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 const uint64_t k0 = 0xc3a5c85c97cb3127ULL;
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static const uint64_t k1 = 0xb492b66fbe98f273ULL;
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static const uint64_t k2 = 0x9ae16a3b2f90404fULL;
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// Magic numbers for 32-bit hashing. Copied from Murmur3.
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static const uint32_t c1 = 0xcc9e2d51;
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static const uint32_t c2 = 0x1b873593;
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// A 32-bit to 32-bit integer hash copied from Murmur3.
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static uint32_t fmix(uint32_t h) {
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h ^= h >> 16;
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h *= 0x85ebca6b;
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h ^= h >> 13;
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h *= 0xc2b2ae35;
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h ^= h >> 16;
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return h;
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}
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static uint32_t Rotate32(uint32_t val, int shift) {
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// Avoid shifting by 32: doing so yields an undefined result.
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return shift == 0 ? val : ((val >> shift) | (val << (32 - shift)));
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}
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#undef PERMUTE3
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#define PERMUTE3(a, b, c) \
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do { \
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std::swap(a, b); \
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std::swap(a, c); \
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} while (0)
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static uint32_t Mur(uint32_t a, uint32_t h) {
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// Helper from Murmur3 for combining two 32-bit values.
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a *= c1;
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a = Rotate32(a, 17);
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a *= c2;
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h ^= a;
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h = Rotate32(h, 19);
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return h * 5 + 0xe6546b64;
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}
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static uint32_t Hash32Len13to24(const char *s, size_t len) {
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uint32_t a = Fetch32(s - 4 + (len >> 1));
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uint32_t b = Fetch32(s + 4);
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uint32_t c = Fetch32(s + len - 8);
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uint32_t d = Fetch32(s + (len >> 1));
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uint32_t e = Fetch32(s);
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uint32_t f = Fetch32(s + len - 4);
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uint32_t h = len;
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return fmix(Mur(f, Mur(e, Mur(d, Mur(c, Mur(b, Mur(a, h)))))));
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}
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static uint32_t Hash32Len0to4(const char *s, size_t len) {
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uint32_t b = 0;
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uint32_t c = 9;
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for (size_t i = 0; i < len; i++) {
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signed char v = s[i];
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b = b * c1 + v;
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c ^= b;
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}
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return fmix(Mur(b, Mur(len, c)));
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}
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static uint32_t Hash32Len5to12(const char *s, size_t len) {
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uint32_t a = len, b = len * 5, c = 9, d = b;
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a += Fetch32(s);
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b += Fetch32(s + len - 4);
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c += Fetch32(s + ((len >> 1) & 4));
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return fmix(Mur(c, Mur(b, Mur(a, d))));
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}
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uint32_t CityHash32(const char *s, size_t len) {
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if (len <= 24) {
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return len <= 12
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? (len <= 4 ? Hash32Len0to4(s, len) : Hash32Len5to12(s, len))
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: Hash32Len13to24(s, len);
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}
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// len > 24
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uint32_t h = len, g = c1 * len, f = g;
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uint32_t a0 = Rotate32(Fetch32(s + len - 4) * c1, 17) * c2;
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uint32_t a1 = Rotate32(Fetch32(s + len - 8) * c1, 17) * c2;
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uint32_t a2 = Rotate32(Fetch32(s + len - 16) * c1, 17) * c2;
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uint32_t a3 = Rotate32(Fetch32(s + len - 12) * c1, 17) * c2;
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uint32_t a4 = Rotate32(Fetch32(s + len - 20) * c1, 17) * c2;
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h ^= a0;
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h = Rotate32(h, 19);
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h = h * 5 + 0xe6546b64;
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h ^= a2;
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h = Rotate32(h, 19);
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h = h * 5 + 0xe6546b64;
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g ^= a1;
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g = Rotate32(g, 19);
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g = g * 5 + 0xe6546b64;
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g ^= a3;
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g = Rotate32(g, 19);
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g = g * 5 + 0xe6546b64;
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f += a4;
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f = Rotate32(f, 19);
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f = f * 5 + 0xe6546b64;
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size_t iters = (len - 1) / 20;
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do {
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uint32_t b0 = Rotate32(Fetch32(s) * c1, 17) * c2;
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uint32_t b1 = Fetch32(s + 4);
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uint32_t b2 = Rotate32(Fetch32(s + 8) * c1, 17) * c2;
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uint32_t b3 = Rotate32(Fetch32(s + 12) * c1, 17) * c2;
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uint32_t b4 = Fetch32(s + 16);
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h ^= b0;
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h = Rotate32(h, 18);
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h = h * 5 + 0xe6546b64;
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f += b1;
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f = Rotate32(f, 19);
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f = f * c1;
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g += b2;
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g = Rotate32(g, 18);
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g = g * 5 + 0xe6546b64;
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h ^= b3 + b1;
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h = Rotate32(h, 19);
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h = h * 5 + 0xe6546b64;
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g ^= b4;
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g = absl::gbswap_32(g) * 5;
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h += b4 * 5;
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h = absl::gbswap_32(h);
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f += b0;
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PERMUTE3(f, h, g);
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s += 20;
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} while (--iters != 0);
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g = Rotate32(g, 11) * c1;
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g = Rotate32(g, 17) * c1;
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f = Rotate32(f, 11) * c1;
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f = Rotate32(f, 17) * c1;
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h = Rotate32(h + g, 19);
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h = h * 5 + 0xe6546b64;
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h = Rotate32(h, 17) * c1;
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h = Rotate32(h + f, 19);
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h = h * 5 + 0xe6546b64;
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h = Rotate32(h, 17) * c1;
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return h;
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}
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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 uint64_t Rotate(uint64_t 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 uint64_t ShiftMix(uint64_t val) { return val ^ (val >> 47); }
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static uint64_t HashLen16(uint64_t u, uint64_t v, uint64_t mul) {
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// Murmur-inspired hashing.
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uint64_t a = (u ^ v) * mul;
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a ^= (a >> 47);
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uint64_t 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 uint64_t HashLen16(uint64_t u, uint64_t v) {
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const uint64_t kMul = 0x9ddfea08eb382d69ULL;
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return HashLen16(u, v, kMul);
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}
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static uint64_t HashLen0to16(const char *s, size_t len) {
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if (len >= 8) {
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uint64_t mul = k2 + len * 2;
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uint64_t a = Fetch64(s) + k2;
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uint64_t b = Fetch64(s + len - 8);
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uint64_t c = Rotate(b, 37) * mul + a;
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uint64_t 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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uint64_t mul = k2 + len * 2;
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uint64_t 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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uint8_t a = s[0];
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uint8_t b = s[len >> 1];
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uint8_t c = s[len - 1];
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uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8);
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uint32_t z = len + (static_cast<uint32_t>(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 uint64_t HashLen17to32(const char *s, size_t len) {
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uint64_t mul = k2 + len * 2;
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uint64_t a = Fetch64(s) * k1;
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uint64_t b = Fetch64(s + 8);
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uint64_t c = Fetch64(s + len - 8) * mul;
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uint64_t d = Fetch64(s + len - 16) * k2;
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return HashLen16(Rotate(a + b, 43) + Rotate(c, 30) + d,
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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 std::pair<uint64_t, uint64_t> WeakHashLen32WithSeeds(
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uint64_t w, uint64_t x, uint64_t y, uint64_t z, uint64_t a, uint64_t b) {
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a += w;
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b = Rotate(b + a + z, 21);
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uint64_t 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 std::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 std::pair<uint64_t, uint64_t> WeakHashLen32WithSeeds(const char *s,
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uint64_t a,
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uint64_t b) {
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return WeakHashLen32WithSeeds(Fetch64(s), Fetch64(s + 8), Fetch64(s + 16),
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Fetch64(s + 24), a, b);
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}
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// Return an 8-byte hash for 33 to 64 bytes.
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static uint64_t HashLen33to64(const char *s, size_t len) {
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uint64_t mul = k2 + len * 2;
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uint64_t a = Fetch64(s) * k2;
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uint64_t b = Fetch64(s + 8);
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uint64_t c = Fetch64(s + len - 24);
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uint64_t d = Fetch64(s + len - 32);
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uint64_t e = Fetch64(s + 16) * k2;
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uint64_t f = Fetch64(s + 24) * 9;
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uint64_t g = Fetch64(s + len - 8);
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uint64_t h = Fetch64(s + len - 16) * mul;
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uint64_t u = Rotate(a + g, 43) + (Rotate(b, 30) + c) * 9;
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uint64_t v = ((a + g) ^ d) + f + 1;
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uint64_t w = absl::gbswap_64((u + v) * mul) + h;
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uint64_t x = Rotate(e + f, 42) + c;
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uint64_t y = (absl::gbswap_64((v + w) * mul) + g) * mul;
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uint64_t z = e + f + c;
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a = absl::gbswap_64((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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uint64_t 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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uint64_t x = Fetch64(s + len - 40);
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uint64_t y = Fetch64(s + len - 16) + Fetch64(s + len - 56);
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uint64_t z = HashLen16(Fetch64(s + len - 48) + len, Fetch64(s + len - 24));
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std::pair<uint64_t, uint64_t> v =
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WeakHashLen32WithSeeds(s + len - 64, len, z);
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std::pair<uint64_t, uint64_t> w =
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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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uint64_t CityHash64WithSeed(const char *s, size_t len, uint64_t seed) {
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return CityHash64WithSeeds(s, len, k2, seed);
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}
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uint64_t CityHash64WithSeeds(const char *s, size_t len, uint64_t seed0,
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uint64_t seed1) {
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return HashLen16(CityHash64(s, len) - seed0, seed1);
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}
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} // namespace hash_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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