diff options
Diffstat (limited to 'absl/hash')
| -rw-r--r-- | absl/hash/internal/hash.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h index 69dbbc6b..90627e00 100644 --- a/absl/hash/internal/hash.h +++ b/absl/hash/internal/hash.h @@ -856,8 +856,15 @@ 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 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 |