diff options
Diffstat (limited to 'absl/crc/internal/crc_x86_arm_combined.cc')
| -rw-r--r-- | absl/crc/internal/crc_x86_arm_combined.cc | 18 |
1 files changed, 11 insertions, 7 deletions
diff --git a/absl/crc/internal/crc_x86_arm_combined.cc b/absl/crc/internal/crc_x86_arm_combined.cc index 51eff4ed..79dace34 100644 --- a/absl/crc/internal/crc_x86_arm_combined.cc +++ b/absl/crc/internal/crc_x86_arm_combined.cc @@ -101,13 +101,17 @@ constexpr size_t kMediumCutoff = 2048; namespace { uint32_t multiply(uint32_t a, uint32_t b) { - V128 shifts = V128_From2x64(0, 1); - V128 power = V128_From2x64(0, a); - V128 crc = V128_From2x64(0, b); + V128 power = V128_From64WithZeroFill(a); + V128 crc = V128_From64WithZeroFill(b); V128 res = V128_PMulLow(power, crc); - // Combine crc values - res = V128_ShiftLeft64(res, shifts); + // Combine crc values. + // + // Adding res to itself is equivalent to multiplying by 2, + // or shifting left by 1. Addition is used as not all compilers + // are able to generate optimal code without this hint. + // https://godbolt.org/z/rr3fMnf39 + res = V128_Add64(res, res); return static_cast<uint32_t>(V128_Extract32<1>(res)) ^ CRC32_u32(0, static_cast<uint32_t>(V128_Low64(res))); } @@ -444,11 +448,11 @@ class CRC32AcceleratedX86ARMCombinedMultipleStreams V128 magic = *(reinterpret_cast<const V128*>(kClmulConstants) + bs - 1); - V128 tmp = V128_From2x64(0, l64); + V128 tmp = V128_From64WithZeroFill(l64); V128 res1 = V128_PMulLow(tmp, magic); - tmp = V128_From2x64(0, l641); + tmp = V128_From64WithZeroFill(l641); V128 res2 = V128_PMul10(tmp, magic); V128 x = V128_Xor(res1, res2); |