Changes imported from Abseil "staging" branch:

  - 3f758237a43af1f277990492701d26d1153b4d74 Generalize the construction/destruction tests, to prepare... by Greg Falcon <gfalcon@google.com>
  - 7bea88f74fbac34b0c0b00b8b832a544988b9465 Simplify non intrinsic uint128 multiply. by Alex Strelnikov <strel@google.com>

GitOrigin-RevId: 3f758237a43af1f277990492701d26d1153b4d74
Change-Id: Idd9a2df0b90403f10f56bb66d30b76a8ba9f50e7

1 files changed, 2 insertions, 13 deletions

diff --git a/absl/numeric/int128.h b/absl/numeric/int128.h
index 94d2f7ce2985..5e1b3f03c0f2 100644
--- a/absl/numeric/int128.h
+++ b/absl/numeric/int128.h
@@ -570,25 +570,14 @@ inline uint128& uint128::operator*=(uint128 other) {
           static_cast<unsigned __int128>(other);
   return *this;
 #else   // ABSL_HAVE_INTRINSIC128
-  uint64_t a96 = hi_ >> 32;
-  uint64_t a64 = hi_ & 0xffffffff;
   uint64_t a32 = lo_ >> 32;
   uint64_t a00 = lo_ & 0xffffffff;
-  uint64_t b96 = other.hi_ >> 32;
-  uint64_t b64 = other.hi_ & 0xffffffff;
   uint64_t b32 = other.lo_ >> 32;
   uint64_t b00 = other.lo_ & 0xffffffff;
-  // multiply [a96 .. a00] x [b96 .. b00]
-  // terms higher than c96 disappear off the high side
-  // terms c96 and c64 are safe to ignore carry bit
-  uint64_t c96 = a96 * b00 + a64 * b32 + a32 * b64 + a00 * b96;
-  uint64_t c64 = a64 * b00 + a32 * b32 + a00 * b64;
-  this->hi_ = (c96 << 32) + c64;
-  this->lo_ = 0;
-  // add terms after this one at a time to capture carry
+  hi_ = hi_ * other.lo_ + lo_ * other.hi_ + a32 * b32;
+  lo_ = a00 * b00;
   *this += uint128(a32 * b00) << 32;
   *this += uint128(a00 * b32) << 32;
-  *this += a00 * b00;
   return *this;
 #endif  // ABSL_HAVE_INTRINSIC128
 }