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Fix a problem with APFloat::roundToIntegral where it would return incorrect results for negative inputs to trunc. Add unit tests to verify this behavior. 

llvm-svn: 161929
This commit is contained in:
Owen Anderson 2012-08-15 05:39:46 +00:00
parent 1049611070
commit 1ff74b0d2d
2 changed files with 42 additions and 0 deletions
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12
llvm/lib/Support/APFloat.cpp
View File

@ -1774,19 +1774,31 @@ APFloat::opStatus APFloat::roundToIntegral(roundingMode rounding_mode) {
// precision of our format, and then subtract it back off again. The choice
// of rounding modes for the addition/subtraction determines the rounding mode
// for our integral rounding as well.
// NOTE: When the input value is negative, we do subtractation followed by
// addition instead.
APInt IntegerConstant(NextPowerOf2(semanticsPrecision(*semantics)), 1);
IntegerConstant <<= semanticsPrecision(*semantics)-1;
APFloat MagicConstant(*semantics);
fs = MagicConstant.convertFromAPInt(IntegerConstant, false,
rmNearestTiesToEven);
MagicConstant.copySign(*this);
if (fs != opOK)
return fs;
// Preserve the input sign so that we can handle 0.0/-0.0 cases correctly.
bool inputSign = isNegative();
fs = add(MagicConstant, rounding_mode);
if (fs != opOK && fs != opInexact)
return fs;
fs = subtract(MagicConstant, rounding_mode);
// Restore the input sign.
if (inputSign != isNegative())
changeSign();
return fs;
}

30
llvm/unittests/ADT/APFloatTest.cpp
View File

@ -648,6 +648,36 @@ TEST(APFloatTest, exactInverse) {
EXPECT_FALSE(APFloat(1.40129846e-45f).getExactInverse(0));
}
TEST(APFloatTest, roundToIntegral) {
APFloat T(-0.5), S(3.14), P(0.0);
P = T;
P.roundToIntegral(APFloat::rmTowardZero);
EXPECT_EQ(-0.0, P.convertToDouble());
P = T;
P.roundToIntegral(APFloat::rmTowardNegative);
EXPECT_EQ(-1.0, P.convertToDouble());
P = T;
P.roundToIntegral(APFloat::rmTowardPositive);
EXPECT_EQ(-0.0, P.convertToDouble());
P = T;
P.roundToIntegral(APFloat::rmNearestTiesToEven);
EXPECT_EQ(-0.0, P.convertToDouble());
P = S;
P.roundToIntegral(APFloat::rmTowardZero);
EXPECT_EQ(3.0, P.convertToDouble());
P = S;
P.roundToIntegral(APFloat::rmTowardNegative);
EXPECT_EQ(3.0, P.convertToDouble());
P = S;
P.roundToIntegral(APFloat::rmTowardPositive);
EXPECT_EQ(4.0, P.convertToDouble());
P = S;
P.roundToIntegral(APFloat::rmNearestTiesToEven);
EXPECT_EQ(3.0, P.convertToDouble());
}
TEST(APFloatTest, getLargest) {
EXPECT_EQ(3.402823466e+38f, APFloat::getLargest(APFloat::IEEEsingle).convertToFloat());
EXPECT_EQ(1.7976931348623158e+308, APFloat::getLargest(APFloat::IEEEdouble).convertToDouble());