Creation of LTS branch "lts_2018_12_18"20181200

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GitOrigin-RevId: 44b0fafc62d9b8f192e8180cbe9c4b806b339d57
Change-Id: I2c427b5b41b2d34101922048b00f3d9dafcb498d

1 files changed, 346 insertions, 0 deletions

diff --git a/absl/hash/internal/city.cc b/absl/hash/internal/city.cc
new file mode 100644
index 00000000..5c076fb5
--- /dev/null
+++ b/absl/hash/internal/city.cc
@@ -0,0 +1,346 @@
+// 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
+//
+//      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.
+//
+// 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 {
+inline namespace lts_2018_12_18 {
+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) {
+  return Hash128to64(uint128(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 = 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
+}  // inline namespace lts_2018_12_18
+}  // namespace absl