// 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 = static_cast<uint32_t>(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 = static_cast<signed char>(s[i]);

    b = b * c1 + static_cast<uint32_t>(v);

    c ^= b;

  }

  return fmix(Mur(b, Mur(static_cast<uint32_t>(len), c)));

}

static uint32_t Hash32Len5to12(const char *s, size_t len) {

  uint32_t a = static_cast<uint32_t>(len), b = a * 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 = static_cast<uint32_t>(len), g = c1 * h, 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 = static_cast<uint8_t>(s[0]);

    uint8_t b = static_cast<uint8_t>(s[len >> 1]);

    uint8_t c = static_cast<uint8_t>(s[len - 1]);

    uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8);

    uint32_t z = static_cast<uint32_t>(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