Export of internal Abseil changes

--
fcedaa5714efab8738446fa21620b827a40a3458 by Derek Mauro <dmauro@google.com>:

Uses Wyhash in the implementation of absl::Hash for hashing sequences
of more than 16 bytes on some platforms.

Due to the per-process randomization of the seed used by absl::Hash, users
should not notice this change, other than possibly getting better performance.

This change only affects platforms where absl::uint128 is implemented
with an intrinsic (and where sizeof(size_t)==8) since Wyhash relies on
fast 128-bit multiplication for speed.

PiperOrigin-RevId: 343956735

--
085e108c760084f19caa21dbeb2118de2be3f8f0 by Abseil Team <absl-team@google.com>:

Internal change for cord ring

PiperOrigin-RevId: 343919274

--
4c333278ad14d6692f203074b902506008ad624a by Jorg Brown <jorg@google.com>:

Minimize strings_internal::StringConstant further, by removing the need for the compiler to instantiate a compile-time class function.

PiperOrigin-RevId: 343878568

--
71c3c8c7b7821b67997e3d5345aaec67f93f266f by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 343838259
GitOrigin-RevId: fcedaa5714efab8738446fa21620b827a40a3458
Change-Id: Ifb91895a82d11e743acd42fe97ab7fb70712b7df

1 files changed, 25 insertions, 10 deletions

diff --git a/absl/hash/internal/hash.cc b/absl/hash/internal/hash.cc
index b44ecb3a..1433eb9d 100644
--- a/absl/hash/internal/hash.cc
+++ b/absl/hash/internal/hash.cc
@@ -18,9 +18,9 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace hash_internal {
 
-uint64_t CityHashState::CombineLargeContiguousImpl32(uint64_t state,
-                                                     const unsigned char* first,
-                                                     size_t len) {
+uint64_t HashState::CombineLargeContiguousImpl32(uint64_t state,
+                                                 const unsigned char* first,
+                                                 size_t len) {
   while (len >= PiecewiseChunkSize()) {
     state =
         Mix(state, absl::hash_internal::CityHash32(reinterpret_cast<const char*>(first),
@@ -33,13 +33,11 @@ uint64_t CityHashState::CombineLargeContiguousImpl32(uint64_t state,
                                std::integral_constant<int, 4>{});
 }
 
-uint64_t CityHashState::CombineLargeContiguousImpl64(uint64_t state,
-                                                     const unsigned char* first,
-                                                     size_t len) {
+uint64_t HashState::CombineLargeContiguousImpl64(uint64_t state,
+                                                 const unsigned char* first,
+                                                 size_t len) {
   while (len >= PiecewiseChunkSize()) {
-    state =
-        Mix(state, absl::hash_internal::CityHash64(reinterpret_cast<const char*>(first),
-                                         PiecewiseChunkSize()));
+    state = Mix(state, Hash64(first, PiecewiseChunkSize()));
     len -= PiecewiseChunkSize();
     first += PiecewiseChunkSize();
   }
@@ -48,7 +46,24 @@ uint64_t CityHashState::CombineLargeContiguousImpl64(uint64_t state,
                                std::integral_constant<int, 8>{});
 }
 
-ABSL_CONST_INIT const void* const CityHashState::kSeed = &kSeed;
+ABSL_CONST_INIT const void* const HashState::kSeed = &kSeed;
+
+// The salt array used by Wyhash. This array is NOT the mechanism used to make
+// absl::Hash non-deterministic between program invocations.  See `Seed()` for
+// that mechanism.
+//
+// Any random values are fine. These values are just digits from the decimal
+// part of pi.
+// https://en.wikipedia.org/wiki/Nothing-up-my-sleeve_number
+constexpr uint64_t kWyhashSalt[5] = {
+    uint64_t{0x243F6A8885A308D3}, uint64_t{0x13198A2E03707344},
+    uint64_t{0xA4093822299F31D0}, uint64_t{0x082EFA98EC4E6C89},
+    uint64_t{0x452821E638D01377},
+};
+
+uint64_t HashState::WyhashImpl(const unsigned char* data, size_t len) {
+  return Wyhash(data, len, Seed(), kWyhashSalt);
+}
 
 }  // namespace hash_internal
 ABSL_NAMESPACE_END