Luminarys commented on a change in pull request #8279:
URL: https://github.com/apache/arrow/pull/8279#discussion_r497669601
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File path: cpp/src/arrow/util/basic_decimal.cc
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@@ -248,40 +252,67 @@ BasicDecimal128& BasicDecimal128::operator>>=(uint32_t
bits) {
return *this;
}
-BasicDecimal128& BasicDecimal128::operator*=(const BasicDecimal128& right) {
- // Break the left and right numbers into 32 bit chunks
- // so that we can multiply them without overflow.
- const uint64_t L0 = static_cast<uint64_t>(high_bits_) >> 32;
- const uint64_t L1 = static_cast<uint64_t>(high_bits_) & kIntMask;
- const uint64_t L2 = low_bits_ >> 32;
- const uint64_t L3 = low_bits_ & kIntMask;
+namespace {
- const uint64_t R0 = static_cast<uint64_t>(right.high_bits_) >> 32;
- const uint64_t R1 = static_cast<uint64_t>(right.high_bits_) & kIntMask;
- const uint64_t R2 = right.low_bits_ >> 32;
- const uint64_t R3 = right.low_bits_ & kIntMask;
+// TODO: Remove this guard once it's used by BasicDecimal256
+#ifndef ARROW_USE_NATIVE_INT128
+void ExtendAndMultiplyUint64(uint64_t x, uint64_t y, uint64_t* hi, uint64_t*
lo) {
+#ifdef ARROW_USE_NATIVE_INT128
+ const __uint128_t r = static_cast<__uint128_t>(x) * y;
+ *lo = r & kInt64Mask;
+ *hi = r >> 64;
+#else
+ const uint64_t x_lo = x & kIntMask;
+ const uint64_t y_lo = y & kIntMask;
+ const uint64_t x_hi = x >> 32;
+ const uint64_t y_hi = y >> 32;
- uint64_t product = L3 * R3;
- low_bits_ = product & kIntMask;
+ const uint64_t t = x_lo * y_lo;
Review comment:
Done
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