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[flang][runtime] Detect & signal underflow when reading reals #75232

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Merged
merged 1 commit into from
Dec 26, 2023
Merged

[flang][runtime] Detect & signal underflow when reading reals #75232

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1 change: 1 addition & 0 deletions flang/include/flang/Decimal/decimal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,7 @@ enum ConversionResultFlags {
Overflow = 1,
Inexact = 2,
Invalid = 4,
Underflow = 8,
};

struct ConversionToDecimalResult {
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31 changes: 21 additions & 10 deletions flang/lib/Decimal/decimal-to-binary.cpp
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Expand Up @@ -256,12 +256,17 @@ ConversionToBinaryResult<PREC> IntermediateFloat<PREC>::ToBinary(
if (guard != 0) {
flags |= Inexact;
}
if (fraction == 0 && guard <= oneHalf) {
if ((!isNegative && rounding == RoundUp) ||
(isNegative && rounding == RoundDown)) {
// round to minimum nonzero value
} else {
return {Binary{}, static_cast<enum ConversionResultFlags>(flags)};
if (fraction == 0) {
if (guard <= oneHalf) {
if ((!isNegative && rounding == RoundUp) ||
(isNegative && rounding == RoundDown)) {
// round to minimum nonzero value
} else { // round to zero
if (guard != 0) {
flags |= Underflow;
}
return {Binary{}, static_cast<enum ConversionResultFlags>(flags)};
}
}
} else {
// The value is nonzero; normalize it.
Expand Down Expand Up @@ -301,8 +306,10 @@ ConversionToBinaryResult<PREC> IntermediateFloat<PREC>::ToBinary(
}
if (expo == 1 && fraction < topBit) {
expo = 0; // subnormal
}
if (expo >= Binary::maxExponent) {
flags |= Underflow;
} else if (expo == 0) {
flags |= Underflow;
} else if (expo >= Binary::maxExponent) {
expo = Binary::maxExponent; // Inf
flags |= Overflow;
if constexpr (Binary::bits == 80) { // x87
Expand Down Expand Up @@ -338,11 +345,15 @@ BigRadixFloatingPointNumber<PREC, LOG10RADIX>::ConvertToBinary() {
// Sanity checks for ridiculous exponents
static constexpr int crazy{2 * Real::decimalRange + log10Radix};
if (exponent_ < -crazy) {
enum ConversionResultFlags flags {
static_cast<enum ConversionResultFlags>(Inexact | Underflow)
};
if ((!isNegative_ && rounding_ == RoundUp) ||
(isNegative_ && rounding_ == RoundDown)) {
return {Real{Raw{1} | SignBit()}}; // return least nonzero value
// return least nonzero value
return {Real{Raw{1} | SignBit()}, flags};
} else { // underflow to +/-0.
return {Real{SignBit()}, Inexact};
return {Real{SignBit()}, flags};
}
} else if (exponent_ > crazy) { // overflow to +/-Inf.
return {Real{Infinity()}, Overflow};
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7 changes: 6 additions & 1 deletion flang/runtime/edit-input.cpp
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Expand Up @@ -478,6 +478,9 @@ static void RaiseFPExceptions(decimal::ConversionResultFlags flags) {
if (flags & decimal::ConversionResultFlags::Overflow) {
RAISE(FE_OVERFLOW);
}
if (flags & decimal::ConversionResultFlags::Underflow) {
RAISE(FE_UNDERFLOW);
}
if (flags & decimal::ConversionResultFlags::Inexact) {
RAISE(FE_INEXACT);
}
Expand Down Expand Up @@ -640,10 +643,12 @@ decimal::ConversionToBinaryResult<binaryPrecision> ConvertHexadecimal(
}
// Package & return result
constexpr RawType significandMask{(one << RealType::significandBits) - 1};
int flags{(roundingBit | guardBit) ? decimal::Inexact : decimal::Exact};
if (!fraction) {
expo = 0;
} else if (expo == 1 && !(fraction >> (binaryPrecision - 1))) {
expo = 0; // subnormal
flags |= decimal::Underflow;
} else if (expo >= RealType::maxExponent) {
expo = RealType::maxExponent; // +/-Inf
fraction = 0;
Expand All @@ -653,7 +658,7 @@ decimal::ConversionToBinaryResult<binaryPrecision> ConvertHexadecimal(
return decimal::ConversionToBinaryResult<binaryPrecision>{
RealType{static_cast<RawType>(signBit |
static_cast<RawType>(expo) << RealType::significandBits | fraction)},
(roundingBit | guardBit) ? decimal::Inexact : decimal::Exact};
static_cast<enum decimal::ConversionResultFlags>(flags)};
}

template <int KIND>
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