Refactor: define CombineRawImpl for repeated `Mix(state ^ value, kMul)` operations.

PiperOrigin-RevId: 777635780
Change-Id: I7b7305fd27ae552f8b96cc93adb3593385381089

absl/hash/internal/hash.cc

diff --git a/absl/hash/internal/hash.cc b/absl/hash/internal/hash.cc
index 8dcc5bd..a693d5c 100644
--- a/absl/hash/internal/hash.cc
+++ b/absl/hash/internal/hash.cc
@@ -101,9 +101,9 @@
     const unsigned char* data, size_t len, uint64_t state) {
   // TODO(b/417141985): expose and use CityHash32WithSeed.
   // Note: we can't use PrecombineLengthMix here because len can be up to 1024.
-  return Mix((state + len) ^ hash_internal::CityHash32(
-                                 reinterpret_cast<const char*>(data), len),
-             kMul);
+  return CombineRawImpl(
+      state + len,
+      hash_internal::CityHash32(reinterpret_cast<const char*>(data), len));
 }
 
 ABSL_ATTRIBUTE_NOINLINE uint64_t

absl/hash/internal/hash.h

diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h
index 8fd9e97..21728b0 100644
--- a/absl/hash/internal/hash.h
+++ b/absl/hash/internal/hash.h
@@ -1034,6 +1034,11 @@
   return mem0 | mem1;
 }
 
+ABSL_ATTRIBUTE_ALWAYS_INLINE inline uint64_t CombineRawImpl(uint64_t state,
+                                                            uint64_t value) {
+  return Mix(state ^ value, kMul);
+}
+
 // Slow dispatch path for calls to CombineContiguousImpl with a size argument
 // larger than inlined size. Has the same effect as calling
 // CombineContiguousImpl() repeatedly with the chunk stride size.
@@ -1055,7 +1060,7 @@
     // Empty string must modify the state.
     v = 0x57;
   }
-  return Mix(state ^ v, kMul);
+  return CombineRawImpl(state, v);
 }
 
 ABSL_ATTRIBUTE_ALWAYS_INLINE inline uint64_t CombineContiguousImpl9to16(
@@ -1263,7 +1268,7 @@
   template <typename T, absl::enable_if_t<IntegralFastPath<T>::value, int> = 0>
   static size_t hash_with_seed(T value, size_t seed) {
     return static_cast<size_t>(
-        Mix(seed ^ static_cast<std::make_unsigned_t<T>>(value), kMul));
+        CombineRawImpl(seed, static_cast<std::make_unsigned_t<T>>(value)));
   }
 
   template <typename T, absl::enable_if_t<!IntegralFastPath<T>::value, int> = 0>
@@ -1301,7 +1306,7 @@
   // optimize Read1To3 and Read4To8 differently for the string case.
   static MixingHashState combine_raw(MixingHashState hash_state,
                                      uint64_t value) {
-    return MixingHashState(Mix(hash_state.state_ ^ value, kMul));
+    return MixingHashState(CombineRawImpl(hash_state.state_, value));
   }
 
   static MixingHashState combine_weakly_mixed_integer(