diff options
| -rw-r--r-- | absl/hash/internal/hash.h | 9 |
1 files changed, 2 insertions, 7 deletions
diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h index f8103334..45dfdd46 100644 --- a/absl/hash/internal/hash.h +++ b/absl/hash/internal/hash.h @@ -1090,15 +1090,10 @@ class ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> { } ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Mix(uint64_t state, uint64_t v) { -#if defined(__aarch64__) - // On AArch64, calculating a 128-bit product is inefficient, because it - // requires a sequence of two instructions to calculate the upper and lower - // halves of the result. - using MultType = uint64_t; -#else + // Though the 128-bit product on AArch64 needs two instructions, it is + // still a good balance between speed and hash quality. using MultType = absl::conditional_t<sizeof(size_t) == 4, uint64_t, uint128>; -#endif // We do the addition in 64-bit space to make sure the 128-bit // multiplication is fast. If we were to do it as MultType the compiler has // to assume that the high word is non-zero and needs to perform 2 |