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fix: Fix incorrect result from casting double to decimal #12600

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fix: Fix incorrect result from casting double to decimal #12600

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30 changes: 22 additions & 8 deletions velox/type/DecimalUtil.h
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Original file line number Diff line number Diff line change
Expand Up @@ -258,17 +258,31 @@ class DecimalUtil {
// LONG_DOUBLE_MAX.
long double scaledValue = std::round(
(long double)value * DecimalUtil::kPowersOfTen[fractionDigits]);
if (scale > fractionDigits) {
scaledValue *= DecimalUtil::kPowersOfTen[scale - fractionDigits];
} else {
scaledValue /= DecimalUtil::kPowersOfTen[fractionDigits - scale];
}

const auto result = folly::tryTo<TOutput>(std::round(scaledValue));
const auto result = folly::tryTo<TOutput>(scaledValue);
if (result.hasError()) {
return Status::UserError("Result overflows.");
}
const TOutput rescaledValue = result.value();
TOutput rescaledValue = result.value();
if (scale > fractionDigits) {
bool isOverflow = __builtin_mul_overflow(
rescaledValue,
DecimalUtil::kPowersOfTen[scale - fractionDigits],
&rescaledValue);
if (isOverflow) {
return Status::UserError("Result overflows.");
}
} else if (fractionDigits > scale) {
const auto scalingFactor =
DecimalUtil::kPowersOfTen[fractionDigits - scale];
const TOutput remainder = rescaledValue % scalingFactor;
rescaledValue /= scalingFactor;
if (rescaledValue >= 0 && remainder >= scalingFactor / 2) {
++rescaledValue;
} else if (remainder <= -scalingFactor / 2) {
--rescaledValue;
}
}

if (!valueInPrecisionRange<TOutput>(rescaledValue, precision)) {
return Status::UserError(
"Result cannot fit in the given precision {}.", precision);
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2 changes: 2 additions & 0 deletions velox/type/tests/DecimalTest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -396,6 +396,8 @@ TEST(DecimalTest, rescaleDouble) {
assertRescaleDouble(
10.03, DECIMAL(38, 18), HugeInt::parse("1003" + zeros(16)));
assertRescaleDouble(0.034567890, DECIMAL(38, 18), 34'567'890'000'000'000);
assertRescaleDouble(
0.03456789, DECIMAL(38, 33), HugeInt::parse("3456789" + zeros(25)));
assertRescaleDouble(
0.999999999999999, DECIMAL(38, 18), 999'999'999'999'999'000);
assertRescaleDouble(
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