Fix APFloat mod sign

Serguei Katkov · Serguei Katkov · commit f2c2851efe05 · 2017-11-01T07:56:55.000Z
fmod specification requires the sign of the remainder is the same as numerator in case remainder is zero. Reviewers: gottesmm, scanon, arsenm, davide, craig.topper Reviewed By: scanon Subscribers: wdng, llvm-commits Differential Revision: https://reviews.llvm.org/D39225 llvm-svn: 317081
diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
@@ -1743,6 +1743,7 @@ IEEEFloat::opStatus IEEEFloat::remainder(const IEEEFloat &rhs) {
 IEEEFloat::opStatus IEEEFloat::mod(const IEEEFloat &rhs) {
   opStatus fs;
   fs = modSpecials(rhs);
+  unsigned int origSign = sign;
 
   while (isFiniteNonZero() && rhs.isFiniteNonZero() &&
          compareAbsoluteValue(rhs) != cmpLessThan) {
@@ -1754,6 +1755,8 @@ IEEEFloat::opStatus IEEEFloat::mod(const IEEEFloat &rhs) {
     fs = subtract(V, rmNearestTiesToEven);
     assert(fs==opOK);
   }
+  if (isZero())
+    sign = origSign; // fmod requires this
   return fs;
 }
 
diff --git a/llvm/unittests/ADT/APFloatTest.cpp b/llvm/unittests/ADT/APFloatTest.cpp
@@ -3289,6 +3289,20 @@ TEST(APFloatTest, mod) {
     EXPECT_EQ(f1.mod(f2), APFloat::opInvalidOp);
     EXPECT_TRUE(f1.isNaN());
   }
+  {
+    APFloat f1(APFloat::IEEEdouble(), "-4.0");
+    APFloat f2(APFloat::IEEEdouble(), "-2.0");
+    APFloat expected(APFloat::IEEEdouble(), "-0.0");
+    EXPECT_EQ(f1.mod(f2), APFloat::opOK);
+    EXPECT_TRUE(f1.bitwiseIsEqual(expected));
+  }
+  {
+    APFloat f1(APFloat::IEEEdouble(), "-4.0");
+    APFloat f2(APFloat::IEEEdouble(), "2.0");
+    APFloat expected(APFloat::IEEEdouble(), "-0.0");
+    EXPECT_EQ(f1.mod(f2), APFloat::opOK);
+    EXPECT_TRUE(f1.bitwiseIsEqual(expected));
+  }
 }
 
 TEST(APFloatTest, PPCDoubleDoubleAddSpecial) {

Original file line number	Diff line number	Diff line change
`@@ -1743,6 +1743,7 @@ IEEEFloat::opStatus IEEEFloat::remainder(const IEEEFloat &rhs) {`
`1743`	`1743`	`IEEEFloat::opStatus IEEEFloat::mod(const IEEEFloat &rhs) {`
`1744`	`1744`	`opStatus fs;`
`1745`	`1745`	`fs = modSpecials(rhs);`
	`1746`	`+ unsigned int origSign = sign;`
`1746`	`1747`
`1747`	`1748`	`while (isFiniteNonZero() && rhs.isFiniteNonZero() &&`
`1748`	`1749`	`compareAbsoluteValue(rhs) != cmpLessThan) {`
`@@ -1754,6 +1755,8 @@ IEEEFloat::opStatus IEEEFloat::mod(const IEEEFloat &rhs) {`
`1754`	`1755`	`fs = subtract(V, rmNearestTiesToEven);`
`1755`	`1756`	`assert(fs==opOK);`
`1756`	`1757`	`}`
	`1758`	`+ if (isZero())`
	`1759`	`+ sign = origSign; // fmod requires this`
`1757`	`1760`	`return fs;`
`1758`	`1761`	`}`
`1759`	`1762`