path: root/contrib/restricted/abseil-cpp/absl/hash/internal/city.cc

// Copyright 2018 The Abseil Authors. 
// 
// Licensed under the Apache License, Version 2.0 (the "License"); 
// you may not use this file except in compliance with the License. 
// You may obtain a copy of the License at 
// 
//      https://www.apache.org/licenses/LICENSE-2.0 
// 
// Unless required by applicable law or agreed to in writing, software 
// distributed under the License is distributed on an "AS IS" BASIS, 
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
// See the License for the specific language governing permissions and 
// limitations under the License. 
// 
// 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 "absl/hash/internal/city.h" 
 
#include <string.h>  // for memcpy and memset 
#include <algorithm> 
 
#include "absl/base/config.h" 
#include "absl/base/internal/endian.h" 
#include "absl/base/internal/unaligned_access.h" 
#include "absl/base/optimization.h" 
 
namespace absl { 
ABSL_NAMESPACE_BEGIN
namespace hash_internal { 
 
#ifdef ABSL_IS_BIG_ENDIAN 
#define uint32_in_expected_order(x) (absl::gbswap_32(x)) 
#define uint64_in_expected_order(x) (absl::gbswap_64(x)) 
#else 
#define uint32_in_expected_order(x) (x) 
#define uint64_in_expected_order(x) (x) 
#endif 
 
static uint64_t Fetch64(const char *p) { 
  return uint64_in_expected_order(ABSL_INTERNAL_UNALIGNED_LOAD64(p)); 
} 
 
static uint32_t Fetch32(const char *p) { 
  return uint32_in_expected_order(ABSL_INTERNAL_UNALIGNED_LOAD32(p)); 
} 
 
// Some primes between 2^63 and 2^64 for various uses. 
static const uint64_t k0 = 0xc3a5c85c97cb3127ULL; 
static const uint64_t k1 = 0xb492b66fbe98f273ULL; 
static const uint64_t k2 = 0x9ae16a3b2f90404fULL; 
 
// Magic numbers for 32-bit hashing.  Copied from Murmur3. 
static const uint32_t c1 = 0xcc9e2d51; 
static const uint32_t c2 = 0x1b873593; 
 
// A 32-bit to 32-bit integer hash copied from Murmur3. 
static uint32_t fmix(uint32_t h) { 
  h ^= h >> 16; 
  h *= 0x85ebca6b; 
  h ^= h >> 13; 
  h *= 0xc2b2ae35; 
  h ^= h >> 16; 
  return h; 
} 
 
static uint32_t Rotate32(uint32_t val, int shift) { 
  // Avoid shifting by 32: doing so yields an undefined result. 
  return shift == 0 ? val : ((val >> shift) | (val << (32 - shift))); 
} 
 
#undef PERMUTE3 
#define PERMUTE3(a, b, c) \ 
  do {                    \ 
    std::swap(a, b);      \ 
    std::swap(a, c);      \ 
  } while (0) 
 
static uint32_t Mur(uint32_t a, uint32_t h) { 
  // Helper from Murmur3 for combining two 32-bit values. 
  a *= c1; 
  a = Rotate32(a, 17); 
  a *= c2; 
  h ^= a; 
  h = Rotate32(h, 19); 
  return h * 5 + 0xe6546b64; 
} 
 
static uint32_t Hash32Len13to24(const char *s, size_t len) { 
  uint32_t a = Fetch32(s - 4 + (len >> 1)); 
  uint32_t b = Fetch32(s + 4); 
  uint32_t c = Fetch32(s + len - 8); 
  uint32_t d = Fetch32(s + (len >> 1)); 
  uint32_t e = Fetch32(s); 
  uint32_t f = Fetch32(s + len - 4); 
  uint32_t h = len; 
 
  return fmix(Mur(f, Mur(e, Mur(d, Mur(c, Mur(b, Mur(a, h))))))); 
} 
 
static uint32_t Hash32Len0to4(const char *s, size_t len) { 
  uint32_t b = 0; 
  uint32_t c = 9; 
  for (size_t i = 0; i < len; i++) { 
    signed char v = s[i]; 
    b = b * c1 + v; 
    c ^= b; 
  } 
  return fmix(Mur(b, Mur(len, c))); 
} 
 
static uint32_t Hash32Len5to12(const char *s, size_t len) { 
  uint32_t a = len, b = len * 5, c = 9, d = b; 
  a += Fetch32(s); 
  b += Fetch32(s + len - 4); 
  c += Fetch32(s + ((len >> 1) & 4)); 
  return fmix(Mur(c, Mur(b, Mur(a, d)))); 
} 
 
uint32_t CityHash32(const char *s, size_t len) { 
  if (len <= 24) { 
    return len <= 12 
               ? (len <= 4 ? Hash32Len0to4(s, len) : Hash32Len5to12(s, len)) 
               : Hash32Len13to24(s, len); 
  } 
 
  // len > 24 
  uint32_t h = len, g = c1 * len, f = g; 
 
  uint32_t a0 = Rotate32(Fetch32(s + len - 4) * c1, 17) * c2; 
  uint32_t a1 = Rotate32(Fetch32(s + len - 8) * c1, 17) * c2; 
  uint32_t a2 = Rotate32(Fetch32(s + len - 16) * c1, 17) * c2; 
  uint32_t a3 = Rotate32(Fetch32(s + len - 12) * c1, 17) * c2; 
  uint32_t a4 = Rotate32(Fetch32(s + len - 20) * c1, 17) * c2; 
  h ^= a0; 
  h = Rotate32(h, 19); 
  h = h * 5 + 0xe6546b64; 
  h ^= a2; 
  h = Rotate32(h, 19); 
  h = h * 5 + 0xe6546b64; 
  g ^= a1; 
  g = Rotate32(g, 19); 
  g = g * 5 + 0xe6546b64; 
  g ^= a3; 
  g = Rotate32(g, 19); 
  g = g * 5 + 0xe6546b64; 
  f += a4; 
  f = Rotate32(f, 19); 
  f = f * 5 + 0xe6546b64; 
  size_t iters = (len - 1) / 20; 
  do { 
    uint32_t b0 = Rotate32(Fetch32(s) * c1, 17) * c2; 
    uint32_t b1 = Fetch32(s + 4); 
    uint32_t b2 = Rotate32(Fetch32(s + 8) * c1, 17) * c2; 
    uint32_t b3 = Rotate32(Fetch32(s + 12) * c1, 17) * c2; 
    uint32_t b4 = Fetch32(s + 16); 
    h ^= b0; 
    h = Rotate32(h, 18); 
    h = h * 5 + 0xe6546b64; 
    f += b1; 
    f = Rotate32(f, 19); 
    f = f * c1; 
    g += b2; 
    g = Rotate32(g, 18); 
    g = g * 5 + 0xe6546b64; 
    h ^= b3 + b1; 
    h = Rotate32(h, 19); 
    h = h * 5 + 0xe6546b64; 
    g ^= b4; 
    g = absl::gbswap_32(g) * 5; 
    h += b4 * 5; 
    h = absl::gbswap_32(h); 
    f += b0; 
    PERMUTE3(f, h, g); 
    s += 20; 
  } while (--iters != 0); 
  g = Rotate32(g, 11) * c1; 
  g = Rotate32(g, 17) * c1; 
  f = Rotate32(f, 11) * c1; 
  f = Rotate32(f, 17) * c1; 
  h = Rotate32(h + g, 19); 
  h = h * 5 + 0xe6546b64; 
  h = Rotate32(h, 17) * c1; 
  h = Rotate32(h + f, 19); 
  h = h * 5 + 0xe6546b64; 
  h = Rotate32(h, 17) * c1; 
  return h; 
} 
 
// Bitwise right rotate.  Normally this will compile to a single 
// instruction, especially if the shift is a manifest constant. 
static uint64_t Rotate(uint64_t val, int shift) { 
  // Avoid shifting by 64: doing so yields an undefined result. 
  return shift == 0 ? val : ((val >> shift) | (val << (64 - shift))); 
} 
 
static uint64_t ShiftMix(uint64_t val) { return val ^ (val >> 47); } 
 
static uint64_t HashLen16(uint64_t u, uint64_t v, uint64_t mul) { 
  // Murmur-inspired hashing. 
  uint64_t a = (u ^ v) * mul; 
  a ^= (a >> 47); 
  uint64_t b = (v ^ a) * mul; 
  b ^= (b >> 47); 
  b *= mul; 
  return b; 
} 
 
static uint64_t HashLen16(uint64_t u, uint64_t v) {
  const uint64_t kMul = 0x9ddfea08eb382d69ULL;
  return HashLen16(u, v, kMul);
}

static uint64_t HashLen0to16(const char *s, size_t len) { 
  if (len >= 8) { 
    uint64_t mul = k2 + len * 2; 
    uint64_t a = Fetch64(s) + k2; 
    uint64_t b = Fetch64(s + len - 8); 
    uint64_t c = Rotate(b, 37) * mul + a; 
    uint64_t d = (Rotate(a, 25) + b) * mul; 
    return HashLen16(c, d, mul); 
  } 
  if (len >= 4) { 
    uint64_t mul = k2 + len * 2; 
    uint64_t a = Fetch32(s); 
    return HashLen16(len + (a << 3), Fetch32(s + len - 4), mul); 
  } 
  if (len > 0) { 
    uint8_t a = s[0]; 
    uint8_t b = s[len >> 1]; 
    uint8_t c = s[len - 1]; 
    uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8); 
    uint32_t z = len + (static_cast<uint32_t>(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_t HashLen17to32(const char *s, size_t len) { 
  uint64_t mul = k2 + len * 2; 
  uint64_t a = Fetch64(s) * k1; 
  uint64_t b = Fetch64(s + 8); 
  uint64_t c = Fetch64(s + len - 8) * mul; 
  uint64_t 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 std::pair<uint64_t, uint64_t> WeakHashLen32WithSeeds(
    uint64_t w, uint64_t x, uint64_t y, uint64_t z, uint64_t a, uint64_t b) {
  a += w; 
  b = Rotate(b + a + z, 21); 
  uint64_t c = a; 
  a += x; 
  a += y; 
  b += Rotate(a, 44); 
  return std::make_pair(a + z, b + c); 
} 
 
// Return a 16-byte hash for s[0] ... s[31], a, and b.  Quick and dirty. 
static std::pair<uint64_t, uint64_t> WeakHashLen32WithSeeds(const char *s,
                                                            uint64_t a,
                                                            uint64_t 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_t HashLen33to64(const char *s, size_t len) { 
  uint64_t mul = k2 + len * 2; 
  uint64_t a = Fetch64(s) * k2; 
  uint64_t b = Fetch64(s + 8); 
  uint64_t c = Fetch64(s + len - 24); 
  uint64_t d = Fetch64(s + len - 32); 
  uint64_t e = Fetch64(s + 16) * k2; 
  uint64_t f = Fetch64(s + 24) * 9; 
  uint64_t g = Fetch64(s + len - 8); 
  uint64_t h = Fetch64(s + len - 16) * mul; 
  uint64_t u = Rotate(a + g, 43) + (Rotate(b, 30) + c) * 9; 
  uint64_t v = ((a + g) ^ d) + f + 1; 
  uint64_t w = absl::gbswap_64((u + v) * mul) + h; 
  uint64_t x = Rotate(e + f, 42) + c; 
  uint64_t y = (absl::gbswap_64((v + w) * mul) + g) * mul; 
  uint64_t z = e + f + c; 
  a = absl::gbswap_64((x + z) * mul + y) + b; 
  b = ShiftMix((z + a) * mul + d + h) * mul; 
  return b + x; 
} 
 
uint64_t 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_t x = Fetch64(s + len - 40); 
  uint64_t y = Fetch64(s + len - 16) + Fetch64(s + len - 56); 
  uint64_t z = HashLen16(Fetch64(s + len - 48) + len, Fetch64(s + len - 24)); 
  std::pair<uint64_t, uint64_t> v =
      WeakHashLen32WithSeeds(s + len - 64, len, z);
  std::pair<uint64_t, uint64_t> 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_t CityHash64WithSeed(const char *s, size_t len, uint64_t seed) { 
  return CityHash64WithSeeds(s, len, k2, seed); 
} 
 
uint64_t CityHash64WithSeeds(const char *s, size_t len, uint64_t seed0, 
                             uint64_t seed1) {
  return HashLen16(CityHash64(s, len) - seed0, seed1); 
} 
 
}  // namespace hash_internal 
ABSL_NAMESPACE_END
}  // namespace absl