text: /**
   ******************************************************************************
   * Xenia : Xbox 360 Emulator Research Project                                 *
   ******************************************************************************
   * Copyright 2013 Ben Vanik. All rights reserved.                             *
   * Released under the BSD license - see LICENSE in the root for more details. *
   ******************************************************************************
   */
  
  // 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 <xenia/core/hash.h>
  
  #include <string.h>
  #include <algorithm>
  
  namespace xe {
  
  namespace {
  
  typedef std::pair<uint64_t, uint64_t> uint128_t;
  
  inline uint64_t Uint128Low64(const uint128_t &x) { return x.first; }
  inline uint64_t Uint128High64(const uint128_t &x) { return x.second; }
  
  // Hash 128 input bits down to 64 bits of output.
  // This is intended to be a reasonably good hash function.
  inline uint64_t Hash128to64(const uint128_t &x) {
    // Murmur-inspired hashing.
    const uint64_t kMul = 0x9ddfea08eb382d69ULL;
    uint64_t a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul;
    a ^= (a >> 47);
    uint64_t b = (Uint128High64(x) ^ a) * kMul;
    b ^= (b >> 47);
    b *= kMul;
    return b;
  }
  
  inline uint64_t UNALIGNED_LOAD64(const char *p) {
    const uint64_t *p64 = (const uint64_t *)p;
    return *p64;
  }
  inline uint32_t UNALIGNED_LOAD32(const char *p) {
    const uint32_t *p32 = (const uint32_t *)p;
    return *p32;
  }
  
  #if !defined(LIKELY)
  #if HAVE_BUILTIN_EXPECT
  #define LIKELY(x) (__builtin_expect(!!(x), 1))
  #else
  #define LIKELY(x) (x)
  #endif
  #endif
  
  static uint64_t Fetch64(const char *p) { return UNALIGNED_LOAD64(p); }
  
  static uint32_t Fetch32(const char *p) { return 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 = (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 = s[i];
      b = b * c1 + v;
      c ^= b;
    }
    return fmix(Mur(b, Mur((uint32_t)len, c)));
  }
  
  static uint32_t Hash32Len5to12(const char *s, size_t len) {
    uint32_t a = (uint32_t)len, b = (uint32_t)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 = (uint32_t)len, g = c1 * (uint32_t)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 a0 = Rotate32(Fetch32(s) * c1, 17) * c2;
      uint32_t a1 = Fetch32(s + 4);
      uint32_t a2 = Rotate32(Fetch32(s + 8) * c1, 17) * c2;
      uint32_t a3 = Rotate32(Fetch32(s + 12) * c1, 17) * c2;
      uint32_t a4 = Fetch32(s + 16);
      h ^= a0;
      h = Rotate32(h, 18);
      h = h * 5 + 0xe6546b64;
      f += a1;
      f = Rotate32(f, 19);
      f = f * c1;
      g += a2;
      g = Rotate32(g, 18);
      g = g * 5 + 0xe6546b64;
      h ^= a3 + a1;
      h = Rotate32(h, 19);
      h = h * 5 + 0xe6546b64;
      g ^= a4;
      g = poly::byte_swap(g) * 5;
      h += a4 * 5;
      h = poly::byte_swap(h);
      f += a0;
      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) {
    return Hash128to64(uint128_t(u, v));
  }
  
  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 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 = (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 = poly::byte_swap((u + v) * mul) + h;
    uint64_t x = Rotate(e + f, 42) + c;
    uint64_t y = (poly::byte_swap((v + w) * mul) + g) * mul;
    uint64_t z = e + f + c;
    a = poly::byte_swap((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);
  }
  
  }  // anonymous namespace
  
  uint64_t hash64(const void *data, size_t length, uint64_t seed) {
    return HashLen16(CityHash64((const char *)data, length) - k2, seed);
  }
  
  }  // namespace xe