APFloat: x - NaN needs to flip the signbit of NaN when x is a number.

Because we don't have a separate negate( ) function, 0 - NaN does double-duty as the IEEE-754 negate( ) operation, which (unlike most FP ops) *does* attach semantic meaning to the signbit of NaN.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210428 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 27 insertions, 25 deletions

diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index f9fe09541d..7989e30afa 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -1372,7 +1372,9 @@ APFloat::addOrSubtractSpecials(const APFloat &rhs, bool subtract)
   case PackCategoriesIntoKey(fcZero, fcNaN):
   case PackCategoriesIntoKey(fcNormal, fcNaN):
   case PackCategoriesIntoKey(fcInfinity, fcNaN):
-    sign = false;
+    // We need to be sure to flip the sign here for subtraction because we
+    // don't have a separate negate operation so -NaN becomes 0 - NaN here.
+    sign = rhs.sign ^ subtract;
     category = fcNaN;
     copySignificand(rhs);
     return opOK;
diff --git a/unittests/ADT/APFloatTest.cpp b/unittests/ADT/APFloatTest.cpp
index e57c8d4b93..86a48bf6c8 100644
--- a/unittests/ADT/APFloatTest.cpp
+++ b/unittests/ADT/APFloatTest.cpp
@@ -1844,10 +1844,10 @@ TEST(APFloatTest, subtract) {
     { PInf, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { PInf, PZero, "inf", APFloat::opOK, APFloat::fcInfinity },
     { PInf, MZero, "inf", APFloat::opOK, APFloat::fcInfinity },
-    { PInf, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { PInf, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { PInf, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { PInf, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { PInf, PNormalValue, "inf", APFloat::opOK, APFloat::fcInfinity },
     { PInf, MNormalValue, "inf", APFloat::opOK, APFloat::fcInfinity },
@@ -1861,10 +1861,10 @@ TEST(APFloatTest, subtract) {
     { MInf, MInf, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
     { MInf, PZero, "-inf", APFloat::opOK, APFloat::fcInfinity },
     { MInf, MZero, "-inf", APFloat::opOK, APFloat::fcInfinity },
-    { MInf, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { MInf, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { MInf, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { MInf, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { MInf, PNormalValue, "-inf", APFloat::opOK, APFloat::fcInfinity },
     { MInf, MNormalValue, "-inf", APFloat::opOK, APFloat::fcInfinity },
@@ -1878,10 +1878,10 @@ TEST(APFloatTest, subtract) {
     { PZero, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { PZero, PZero, "0x0p+0", APFloat::opOK, APFloat::fcZero },
     { PZero, MZero, "0x0p+0", APFloat::opOK, APFloat::fcZero },
-    { PZero, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { PZero, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { PZero, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { PZero, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { PZero, PNormalValue, "-0x1p+0", APFloat::opOK, APFloat::fcNormal },
     { PZero, MNormalValue, "0x1p+0", APFloat::opOK, APFloat::fcNormal },
@@ -1895,10 +1895,10 @@ TEST(APFloatTest, subtract) {
     { MZero, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { MZero, PZero, "-0x0p+0", APFloat::opOK, APFloat::fcZero },
     { MZero, MZero, "0x0p+0", APFloat::opOK, APFloat::fcZero },
-    { MZero, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { MZero, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { MZero, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { MZero, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { MZero, PNormalValue, "-0x1p+0", APFloat::opOK, APFloat::fcNormal },
     { MZero, MNormalValue, "0x1p+0", APFloat::opOK, APFloat::fcNormal },
@@ -1946,10 +1946,10 @@ TEST(APFloatTest, subtract) {
     { PNormalValue, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { PNormalValue, PZero, "0x1p+0", APFloat::opOK, APFloat::fcNormal },
     { PNormalValue, MZero, "0x1p+0", APFloat::opOK, APFloat::fcNormal },
-    { PNormalValue, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { PNormalValue, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { PNormalValue, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { PNormalValue, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { PNormalValue, PNormalValue, "0x0p+0", APFloat::opOK, APFloat::fcZero },
     { PNormalValue, MNormalValue, "0x1p+1", APFloat::opOK, APFloat::fcNormal },
@@ -1963,10 +1963,10 @@ TEST(APFloatTest, subtract) {
     { MNormalValue, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { MNormalValue, PZero, "-0x1p+0", APFloat::opOK, APFloat::fcNormal },
     { MNormalValue, MZero, "-0x1p+0", APFloat::opOK, APFloat::fcNormal },
-    { MNormalValue, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { MNormalValue, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { MNormalValue, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { MNormalValue, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { MNormalValue, PNormalValue, "-0x1p+1", APFloat::opOK, APFloat::fcNormal },
     { MNormalValue, MNormalValue, "0x0p+0", APFloat::opOK, APFloat::fcZero },
@@ -1980,10 +1980,10 @@ TEST(APFloatTest, subtract) {
     { PLargestValue, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { PLargestValue, PZero, "0x1.fffffep+127", APFloat::opOK, APFloat::fcNormal },
     { PLargestValue, MZero, "0x1.fffffep+127", APFloat::opOK, APFloat::fcNormal },
-    { PLargestValue, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { PLargestValue, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { PLargestValue, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { PLargestValue, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { PLargestValue, PNormalValue, "0x1.fffffep+127", APFloat::opInexact, APFloat::fcNormal },
     { PLargestValue, MNormalValue, "0x1.fffffep+127", APFloat::opInexact, APFloat::fcNormal },
@@ -1997,10 +1997,10 @@ TEST(APFloatTest, subtract) {
     { MLargestValue, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { MLargestValue, PZero, "-0x1.fffffep+127", APFloat::opOK, APFloat::fcNormal },
     { MLargestValue, MZero, "-0x1.fffffep+127", APFloat::opOK, APFloat::fcNormal },
-    { MLargestValue, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { MLargestValue, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { MLargestValue, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { MLargestValue, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { MLargestValue, PNormalValue, "-0x1.fffffep+127", APFloat::opInexact, APFloat::fcNormal },
     { MLargestValue, MNormalValue, "-0x1.fffffep+127", APFloat::opInexact, APFloat::fcNormal },
@@ -2014,10 +2014,10 @@ TEST(APFloatTest, subtract) {
     { PSmallestValue, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { PSmallestValue, PZero, "0x1p-149", APFloat::opOK, APFloat::fcNormal },
     { PSmallestValue, MZero, "0x1p-149", APFloat::opOK, APFloat::fcNormal },
-    { PSmallestValue, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { PSmallestValue, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { PSmallestValue, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { PSmallestValue, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { PSmallestValue, PNormalValue, "-0x1p+0", APFloat::opInexact, APFloat::fcNormal },
     { PSmallestValue, MNormalValue, "0x1p+0", APFloat::opInexact, APFloat::fcNormal },
@@ -2031,10 +2031,10 @@ TEST(APFloatTest, subtract) {
     { MSmallestValue, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { MSmallestValue, PZero, "-0x1p-149", APFloat::opOK, APFloat::fcNormal },
     { MSmallestValue, MZero, "-0x1p-149", APFloat::opOK, APFloat::fcNormal },
-    { MSmallestValue, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { MSmallestValue, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { MSmallestValue, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { MSmallestValue, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { MSmallestValue, PNormalValue, "-0x1p+0", APFloat::opInexact, APFloat::fcNormal },
     { MSmallestValue, MNormalValue, "0x1p+0", APFloat::opInexact, APFloat::fcNormal },
@@ -2048,10 +2048,10 @@ TEST(APFloatTest, subtract) {
     { PSmallestNormalized, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { PSmallestNormalized, PZero, "0x1p-126", APFloat::opOK, APFloat::fcNormal },
     { PSmallestNormalized, MZero, "0x1p-126", APFloat::opOK, APFloat::fcNormal },
-    { PSmallestNormalized, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { PSmallestNormalized, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { PSmallestNormalized, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { PSmallestNormalized, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { PSmallestNormalized, PNormalValue, "-0x1p+0", APFloat::opInexact, APFloat::fcNormal },
     { PSmallestNormalized, MNormalValue, "0x1p+0", APFloat::opInexact, APFloat::fcNormal },
@@ -2065,10 +2065,10 @@ TEST(APFloatTest, subtract) {
     { MSmallestNormalized, MInf, "inf", APFloat::opOK, APFloat::fcInfinity },
     { MSmallestNormalized, PZero, "-0x1p-126", APFloat::opOK, APFloat::fcNormal },
     { MSmallestNormalized, MZero, "-0x1p-126", APFloat::opOK, APFloat::fcNormal },
-    { MSmallestNormalized, QNaN, "nan", APFloat::opOK, APFloat::fcNaN },
+    { MSmallestNormalized, QNaN, "-nan", APFloat::opOK, APFloat::fcNaN },
 #if 0
 // See Note 1.
-    { MSmallestNormalized, SNaN, "nan", APFloat::opInvalidOp, APFloat::fcNaN },
+    { MSmallestNormalized, SNaN, "-nan", APFloat::opInvalidOp, APFloat::fcNaN },
 #endif
     { MSmallestNormalized, PNormalValue, "-0x1p+0", APFloat::opInexact, APFloat::fcNormal },
     { MSmallestNormalized, MNormalValue, "0x1p+0", APFloat::opInexact, APFloat::fcNormal },