City.cpp

// 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 "City.h"

#include <algorithm>
#include <string.h>  // for memcpy and memset

using namespace std;

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;
}

#ifndef __BIG_ENDIAN__

#define uint32_in_expected_order(x) (x)
#define uint64_in_expected_order(x) (x)

#else

#ifdef _MSC_VER
#include <stdlib.h>
#define bswap_32(x) _byteswap_ulong(x)
#define bswap_64(x) _byteswap_uint64(x)

#elif defined(__APPLE__)
// Mac OS X / Darwin features
#include <libkern/OSByteOrder.h>
#define bswap_32(x) OSSwapInt32(x)
#define bswap_64(x) OSSwapInt64(x)

#else
#include <byteswap.h>
#endif

#define uint32_in_expected_order(x) (bswap_32(x))
#define uint64_in_expected_order(x) (bswap_64(x))

#endif  // __BIG_ENDIAN__

#if !defined(LIKELY)
#if defined(__GNUC__) || defined(__INTEL_COMPILER)
#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;
static const uint64 k3 = 0xc949d7c7509e6557ULL;

// 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)));
}

// Equivalent to Rotate(), but requires the second arg to be non-zero.
// On x86-64, and probably others, it's possible for this to compile
// to a single instruction if both args are already in registers.
static uint64 RotateByAtLeast1(uint64 val, int shift) {
  return (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 HashLen0to16(const char *s, size_t len) {
  if (len > 8) {
    uint64 a = Fetch64(s);
    uint64 b = Fetch64(s + len - 8);
    return HashLen16(a, RotateByAtLeast1(b + len, len)) ^ b;
  }
  if (len >= 4) {
    uint64 a = Fetch32(s);
    return HashLen16(len + (a << 3), Fetch32(s + len - 4));
  }
  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 = len + (static_cast<uint32>(c) << 2);
    return ShiftMix(y * k2 ^ z * k3) * 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 a = Fetch64(s) * k1;
  uint64 b = Fetch64(s + 8);
  uint64 c = Fetch64(s + len - 8) * k2;
  uint64 d = Fetch64(s + len - 16) * k0;
  return HashLen16(Rotate(a - b, 43) + Rotate(c, 30) + d,
                   a + Rotate(b ^ k3, 20) - c + len);
}

// 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 z = Fetch64(s + 24);
  uint64 a = Fetch64(s) + (len + Fetch64(s + len - 16)) * k0;
  uint64 b = Rotate(a + z, 52);
  uint64 c = Rotate(a, 37);
  a += Fetch64(s + 8);
  c += Rotate(a, 7);
  a += Fetch64(s + 16);
  uint64 vf = a + z;
  uint64 vs = b + Rotate(a, 31) + c;
  a = Fetch64(s + 16) + Fetch64(s + len - 32);
  z = Fetch64(s + len - 8);
  b = Rotate(a + z, 52);
  c = Rotate(a, 37);
  a += Fetch64(s + len - 24);
  c += Rotate(a, 7);
  a += Fetch64(s + len - 16);
  uint64 wf = a + z;
  uint64 ws = b + Rotate(a, 31) + c;
  uint64 r = ShiftMix((vf + ws) * k2 + (wf + vs) * k0);
  return ShiftMix(r * k0 + vs) * k2;
}

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 = 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;
  z += Rotate(w.first, 37) * 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);
  }
  // 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) {
  if (len >= 16) {
    return CityHash128WithSeed(s + 16,
                               len - 16,
                               uint128(Fetch64(s) ^ k3,
                                       Fetch64(s + 8)));
  } else if (len >= 8) {
    return CityHash128WithSeed(NULL,
                               0,
                               uint128(Fetch64(s) ^ (len * k0),
                                       Fetch64(s + len - 8) ^ k1));
  } else {
    return CityHash128WithSeed(s, len, uint128(k0, k1));
  }
}

#if defined(__SSE4_2__) && defined(__x86_64__)
#include <nmmintrin.h>

// Requires len >= 240.
static void CityHashCrc256Long(const char *s, size_t len,
                               uint32 seed, uint64 *result) {
  uint64 a = Fetch64(s + 56) + k0;
  uint64 b = Fetch64(s + 96) + k0;
  uint64 c = result[0] = HashLen16(b, len);
  uint64 d = result[1] = Fetch64(s + 120) * k0 + len;
  uint64 e = Fetch64(s + 184) + seed;
  uint64 f = seed;
  uint64 g = 0;
  uint64 h = 0;
  uint64 i = 0;
  uint64 j = 0;
  uint64 t = c + d;

  // 240 bytes of input per iter.
  size_t iters = len / 240;
  len -= iters * 240;
  do {
#define CHUNK(multiplier, z)                                    \
    {                                                           \
      uint64 old_a = a;                                         \
      a = Rotate(b, 41 ^ z) * multiplier + Fetch64(s);          \
      b = Rotate(c, 27 ^ z) * multiplier + Fetch64(s + 8);      \
      c = Rotate(d, 41 ^ z) * multiplier + Fetch64(s + 16);     \
      d = Rotate(e, 33 ^ z) * multiplier + Fetch64(s + 24);     \
      e = Rotate(t, 25 ^ z) * multiplier + Fetch64(s + 32);     \
      t = old_a;                                                \
    }                                                           \
    f = _mm_crc32_u64(f, a);                                    \
    g = _mm_crc32_u64(g, b);                                    \
    h = _mm_crc32_u64(h, c);                                    \
    i = _mm_crc32_u64(i, d);                                    \
    j = _mm_crc32_u64(j, e);                                    \
    s += 40

    CHUNK(1, 1); CHUNK(k0, 0);
    CHUNK(1, 1); CHUNK(k0, 0);
    CHUNK(1, 1); CHUNK(k0, 0);
  } while (--iters > 0);

  while (len >= 40) {
    CHUNK(k0, 0);
    len -= 40;
  }
  if (len > 0) {
    s = s + len - 40;
    CHUNK(k0, 0);
  }
  j += i << 32;
  a = HashLen16(a, j);
  h += g << 32;
  b += h;
  c = HashLen16(c, f) + i;
  d = HashLen16(d, e + result[0]);
  j += e;
  i += HashLen16(h, t);
  e = HashLen16(a, d) + j;
  f = HashLen16(b, c) + a;
  g = HashLen16(j, i) + c;
  result[0] = e + f + g + h;
  a = ShiftMix((a + g) * k0) * k0 + b;
  result[1] += a + result[0];
  a = ShiftMix(a * k0) * k0 + c;
  result[2] = a + result[1];
  a = ShiftMix((a + e) * k0) * k0;
  result[3] = a + result[2];
}

// Requires len < 240.
static void CityHashCrc256Short(const char *s, size_t len, uint64 *result) {
  char buf[240];
  memcpy(buf, s, len);
  memset(buf + len, 0, 240 - len);
  CityHashCrc256Long(buf, 240, ~static_cast<uint32>(len), result);
}

void CityHashCrc256(const char *s, size_t len, uint64 *result) {
  if (LIKELY(len >= 240)) {
    CityHashCrc256Long(s, len, 0, result);
  } else {
    CityHashCrc256Short(s, len, result);
  }
}

uint128 CityHashCrc128WithSeed(const char *s, size_t len, uint128 seed) {
  if (len <= 900) {
    return CityHash128WithSeed(s, len, seed);
  } else {
    uint64 result[4];
    CityHashCrc256(s, len, result);
    uint64 u = Uint128High64(seed) + result[0];
    uint64 v = Uint128Low64(seed) + result[1];
    return uint128(HashLen16(u, v + result[2]),
                   HashLen16(Rotate(v, 32), u * k0 + result[3]));
  }
}

uint128 CityHashCrc128(const char *s, size_t len) {
  if (len <= 900) {
    return CityHash128(s, len);
  } else {
    uint64 result[4];
    CityHashCrc256(s, len, result);
    return uint128(result[2], result[3]);
  }
}

#endif