Fix a problem with APFloat::roundToIntegral where it would return incorrect results for negative inputs to trunc. Add unit tests to verify this behavior.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161929 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index 5ea75a6..84021de 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -1774,19 +1774,31 @@
// 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;
}