Fix another roundToIntegral bug where very large values could become infinity. Problem and solution identified by Steve Canon.

llvm-svn: 161969

2 files changed, 20 insertions, 1 deletions

diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
index b42a168bae7..ed261a4194c 100644
--- a/llvm/lib/Support/APFloat.cpp
+++ b/llvm/lib/Support/APFloat.cpp
@@ -1770,6 +1770,12 @@ APFloat::opStatus APFloat::roundToIntegral(roundingMode rounding_mode) {
   opStatus fs;
   assertArithmeticOK(*semantics);
 
+  // If the exponent is large enough, we know that this value is already
+  // integral, and the arithmetic below would potentially cause it to saturate
+  // to +/-Inf.  Bail out early instead.
+  if (exponent+1 >= (int)semanticsPrecision(*semantics))
+    return opOK;
+
   // 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
diff --git a/llvm/unittests/ADT/APFloatTest.cpp b/llvm/unittests/ADT/APFloatTest.cpp
index caa288afaf5..00b62feaeb1 100644
--- a/llvm/unittests/ADT/APFloatTest.cpp
+++ b/llvm/unittests/ADT/APFloatTest.cpp
@@ -649,7 +649,7 @@ TEST(APFloatTest, exactInverse) {
 }
 
 TEST(APFloatTest, roundToIntegral) {
-  APFloat T(-0.5), S(3.14), P(0.0);
+  APFloat T(-0.5), S(3.14), R(APFloat::getLargest(APFloat::IEEEdouble)), P(0.0);
 
   P = T;
   P.roundToIntegral(APFloat::rmTowardZero);
@@ -676,6 +676,19 @@ TEST(APFloatTest, roundToIntegral) {
   P = S;
   P.roundToIntegral(APFloat::rmNearestTiesToEven);
   EXPECT_EQ(3.0, P.convertToDouble());
+
+  P = R;
+  P.roundToIntegral(APFloat::rmTowardZero);
+  EXPECT_EQ(R.convertToDouble(), P.convertToDouble());
+  P = R;
+  P.roundToIntegral(APFloat::rmTowardNegative);
+  EXPECT_EQ(R.convertToDouble(), P.convertToDouble());
+  P = R;
+  P.roundToIntegral(APFloat::rmTowardPositive);
+  EXPECT_EQ(R.convertToDouble(), P.convertToDouble());
+  P = R;
+  P.roundToIntegral(APFloat::rmNearestTiesToEven);
+  EXPECT_EQ(R.convertToDouble(), P.convertToDouble());
 }
 
 TEST(APFloatTest, getLargest) {