YugabyteDB (2.13.0.0-b42, bfc6a6643e7399ac8a0e81d06a3ee6d6571b33ab)

// Copyright 2010 Google Inc. All Rights Reserved.

// Authors: gpike@google.com (Geoff Pike), jyrki@google.com (Jyrki Alakuijala)

//

// This file provides CityHash64() and related functions.

//

// The externally visible functions follow the naming conventions of

// hash.h, where the size of the output is part of the name.  For

// example, CityHash64 returns a 64-bit hash.  The internal helpers do

// not have the return type in their name, but instead have names like

// HashLenXX or HashLenXXtoYY, where XX and YY are input string lengths.

//

// Most of the constants and tricks here were copied from murmur.cc or

// hash.h, or discovered by trial and error.  It's probably possible to further

// optimize the code here by writing a program that systematically explores

// more of the space of possible hash functions, or by using SIMD instructions.

//

// The following only applies to changes made to this file as part of YugaByte development.

//

// Portions Copyright (c) YugaByte, Inc.

//

// 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

//

// http://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.

//

#include "yb/gutil/hash/city.h"

#include <sys/types.h>

#include <glog/logging.h>

#include "yb/gutil/endian.h"

#include "yb/gutil/hash/hash128to64.h"

using std::copy;

using std::max;

using std::min;

using std::swap;

using std::make_pair;

using std::pair;

namespace util_hash {

// Some primes between 2^63 and 2^64 for various uses.

static const uint64 k0 = 0xa5b85c5e198ed849ULL;

static const uint64 k1 = 0x8d58ac26afe12e47ULL;

static const uint64 k2 = 0xc47b6e9e3a970ed3ULL;

static const uint64 k3 = 0xc70f6907e782aa0bULL;

// 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) {

  DCHECK_GE(shift, 0);

  DCHECK_LE(shift, 63);

  // 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, size_t shift) {

  DCHECK_GE(shift, 1);

  DCHECK_LE(shift, 63);

  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) {

  DCHECK_GE(len, 0);

  DCHECK_LE(len, 16);

  if (len > 8) {

    uint64 a = LittleEndian::Load64(s);

    uint64 b = LittleEndian::Load64(s + len - 8);

    return HashLen16(a, RotateByAtLeast1(b + len, len)) ^ b;

  }

  if (len >= 4) {

    uint64 a = LittleEndian::Load32(s);

    return HashLen16(len + (a << 3), LittleEndian::Load32(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 = static_cast<uint32>(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) {

  DCHECK_GE(len, 17);

  DCHECK_LE(len, 32);

  uint64 a = LittleEndian::Load64(s) * k1;

  uint64 b = LittleEndian::Load64(s + 8);

  uint64 c = LittleEndian::Load64(s + len - 8) * k2;

  uint64 d = LittleEndian::Load64(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.

// (For more, see the code review discussion of CL 18799087.)

static pair<uint64, uint64> WeakHashLen32WithSeeds(

    uint64 w, uint64 x, uint64 y, uint64 z, uint64 a, uint64 b) {

  a += w;

  b = Rotate(b + a + z, 51);

  uint64 c = a;

  a += x;

  a += y;

  b += Rotate(a, 23);

  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(LittleEndian::Load64(s),

                                LittleEndian::Load64(s + 8),

                                LittleEndian::Load64(s + 16),

                                LittleEndian::Load64(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 = LittleEndian::Load64(s + 24);

  uint64 a = LittleEndian::Load64(s) +

             (len + LittleEndian::Load64(s + len - 16)) * k0;

  uint64 b = Rotate(a + z, 52);

  uint64 c = Rotate(a, 37);

  a += LittleEndian::Load64(s + 8);

  c += Rotate(a, 7);

  a += LittleEndian::Load64(s + 16);

  uint64 vf = a + z;

  uint64 vs = b + Rotate(a, 31) + c;

  a = LittleEndian::Load64(s + 16) + LittleEndian::Load64(s + len - 32);

  z += LittleEndian::Load64(s + len - 8);

  b = Rotate(a + z, 52);

  c = Rotate(a, 37);

  a += LittleEndian::Load64(s + len - 24);

  c += Rotate(a, 7);

  a += LittleEndian::Load64(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 = LittleEndian::Load64(s + len - 40);

  uint64 y = LittleEndian::Load64(s + len - 16) +

             LittleEndian::Load64(s + len - 56);

  uint64 z = HashLen16(LittleEndian::Load64(s + len - 48) + len,

                       LittleEndian::Load64(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 + LittleEndian::Load64(s);

  // Decrease len to the nearest multiple of 64, and operate on 64-byte chunks.

  len = (len - 1) & ~static_cast<size_t>(63);

  DCHECK_GT(len, 0);

  DCHECK_EQ(len, len / 64 * 64);

  do {

    x = Rotate(x + y + v.first + LittleEndian::Load64(s + 8), 37) * k1;

    y = Rotate(y + v.second + LittleEndian::Load64(s + 48), 42) * k1;

    x ^= w.second;

    y += v.first + LittleEndian::Load64(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 + LittleEndian::Load64(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 ssize_t.  Based on City and Murmur128.

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;

  ssize_t l = len - 16;

  if (l <= 0) {  // len <= 16

    c = b * k1 + HashLen0to16(s, len);

    d = Rotate(a + (len >= 8 ? LittleEndian::Load64(s) : c), 32);

  } else {  // len > 16

    c = HashLen16(LittleEndian::Load64(s + len - 8) + k1, a);

    d = HashLen16(b + len, c + LittleEndian::Load64(s + len - 16));

    a += d;

    do {

      a ^= ShiftMix(LittleEndian::Load64(s) * k1) * k1;

      a *= k1;

      b ^= a;

      c ^= ShiftMix(LittleEndian::Load64(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) {

  // TODO(user): As of February 2011, there's a beta of Murmur3 that would

  // most likely be useful here.  E.g., if (len < 900) return Murmur3(...)

  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 + LittleEndian::Load64(s);

  v.second = Rotate(v.first, 42) * k1 + LittleEndian::Load64(s + 8);

  w.first = Rotate(y + z, 35) * k1 + x;

  w.second = Rotate(x + LittleEndian::Load64(s + 88), 53) * k1;

  // This is similar to the inner loop of CityHash64(), manually unrolled.

  do {

    x = Rotate(x + y + v.first + LittleEndian::Load64(s + 16), 37) * k1;

    y = Rotate(y + v.second + LittleEndian::Load64(s + 48), 42) * k1;

    x ^= w.second;

    y ^= v.first;

    z = Rotate(z ^ w.first, 33);

    v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first);

    w = WeakHashLen32WithSeeds(s + 32, z + w.second, y);

    std::swap(z, x);

    s += 64;

    x = Rotate(x + y + v.first + LittleEndian::Load64(s + 16), 37) * k1;

    y = Rotate(y + v.second + LittleEndian::Load64(s + 48), 42) * k1;

    x ^= w.second;

    y ^= v.first;

    z = Rotate(z ^ w.first, 33);

    v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first);

    w = WeakHashLen32WithSeeds(s + 32, z + w.second, y);

    std::swap(z, x);

    s += 64;

    len -= 128;

  } while (PREDICT_TRUE(len >= 128));

  y += Rotate(w.first, 37) * k0 + z;

  x += Rotate(v.first + z, 49) * 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(y - x, 42) * k0 + v.second;

    w.first += LittleEndian::Load64(s + len - tail_done + 16);

    x = Rotate(x, 49) * k0 + w.first;

    w.first += v.first;

    v = WeakHashLen32WithSeeds(s + len - tail_done, v.first, v.second);

  }

  // At this point our 48 bytes of state should contain more than

  // enough information for a strong 128-bit hash.  We use two

  // different 48-byte-to-8-byte hashes to get a 16-byte final result.

  x = HashLen16(x, v.first);

  y = HashLen16(y, 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(LittleEndian::Load64(s) ^ k3,

                                       LittleEndian::Load64(s + 8)));

  } else if (len >= 8) {

    return CityHash128WithSeed(nullptr,

                               0,

                               uint128(LittleEndian::Load64(s) ^ (len * k0),

                                       LittleEndian::Load64(s + len - 8) ^ k1));

  } else {

    return CityHash128WithSeed(s, len, uint128(k0, k1));

  }

}

}  // namespace util_hash