Add a roundToIntegral method to APFloat, which can be parameterized over various rounding modes. Use this to implement SelectionDAG constant folding of FFLOOR, FCEIL, and FTRUNC.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161807 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index 9f5ca3e..2139df5 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -1765,6 +1765,32 @@
return fs;
}
+/* Rounding-mode corrrect round to integral value. */
+APFloat::opStatus APFloat::roundToIntegral(roundingMode rounding_mode) {
+ opStatus fs;
+ assertArithmeticOK(*semantics);
+
+ // The algorithm here is quite simple: we add 2^(p-1), where p is the
+ // 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.
+ APInt IntegerConstant(NextPowerOf2(semanticsPrecision(*semantics)),
+ 1 << (semanticsPrecision(*semantics)-1));
+ APFloat MagicConstant(*semantics);
+ fs = MagicConstant.convertFromAPInt(IntegerConstant, false,
+ rmNearestTiesToEven);
+ if (fs != opOK)
+ return fs;
+
+ fs = add(MagicConstant, rounding_mode);
+ if (fs != opOK && fs != opInexact)
+ return fs;
+
+ fs = subtract(MagicConstant, rounding_mode);
+ return fs;
+}
+
+
/* Comparison requires normalized numbers. */
APFloat::cmpResult
APFloat::compare(const APFloat &rhs) const