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[poincare/decimal] Fix rounding error when buidling 0.9999...

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This commit is contained in:
Ruben Dashyan
2019-05-15 18:35:04 +02:00
committed by Léa Saviot
parent b5bf3b0bbc
commit 6d4404d4b7
1 changed files with 17 additions and 1 deletions
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18
poincare/src/decimal.cpp
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@@ -287,6 +287,13 @@ Decimal Decimal::Builder(const char * integralPart, int integralPartLength, cons
}
//TODO: set a FLAG to tell that a rounding happened?
bool rounding = integralPartLength > PrintFloat::k_numberOfStoredSignificantDigits && integralPart[PrintFloat::k_numberOfStoredSignificantDigits] >= '5';
/* At this point, the exponent has already been computed. In the very special
* case where all the significant digits of the mantissa are 9, rounding up
* must increment the exponent. For instance, rounding up 0.99...9 (whose
* exponent is -1) yields 1 (whose exponent is 0). To that end, the
* significant digits will be scanned successively to determine whether the
* exponent should be incremented. */
bool incrementExponentAfterRoundingUp = true;
// Cap the length of the integralPart
integralPartLength = integralPartLength > PrintFloat::k_numberOfStoredSignificantDigits ? PrintFloat::k_numberOfStoredSignificantDigits : integralPartLength;
Integer numerator(integralPart, integralPartLength, false);
@@ -301,13 +308,22 @@ Decimal Decimal::Builder(const char * integralPart, int integralPartLength, cons
}
rounding |= integralPartLength+fractionalPartLength > PrintFloat::k_numberOfStoredSignificantDigits && fractionalPart[PrintFloat::k_numberOfStoredSignificantDigits-integralPartLength] >= '5';
fractionalPartLength = integralPartLength+fractionalPartLength > PrintFloat::k_numberOfStoredSignificantDigits ? PrintFloat::k_numberOfStoredSignificantDigits - integralPartLength : fractionalPartLength;
while (incrementExponentAfterRoundingUp && integralPartLength-- > 0) {
incrementExponentAfterRoundingUp = (*(integralPart++) == '9');
}
for (int i = 0; i < fractionalPartLength; i++) {
numerator = Integer::Multiplication(numerator, base);
assert(*fractionalPart >= '0' && *fractionalPart <= '9');
numerator = Integer::Addition(numerator, Integer(*fractionalPart-'0'));
incrementExponentAfterRoundingUp &= (*fractionalPart == '9');
fractionalPart++;
}
numerator = rounding ? Integer::Addition(numerator, Integer(1)) : numerator;
if (rounding) {
numerator = Integer::Addition(numerator, Integer(1));
if (incrementExponentAfterRoundingUp) {
exponent++;
}
}
exponent = numerator.isZero() ? 0 : exponent;
return Decimal::Builder(numerator, exponent);
}