Add APFloat::getExactInverse.
The idea is, that if an ieee 754 float is divided by a power of two, we can
turn the division into a cheaper multiplication. This function sees if we can
get an exact multiplicative inverse for a divisor and returns it if possible.
This is the hard part of PR9587.
I tested many inputs against llvm-gcc's frotend implementation of this
optimization and didn't find any difference. However, floating point is the
land of weird edge cases, so any review would be appreciated.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128545 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/ADT/APFloatTest.cpp b/unittests/ADT/APFloatTest.cpp
index 964b04d..dea4a65 100644
--- a/unittests/ADT/APFloatTest.cpp
+++ b/unittests/ADT/APFloatTest.cpp
@@ -576,4 +576,27 @@
#endif
#endif
+TEST(APFloatTest, exactInverse) {
+ APFloat inv(0.0f);
+
+ // Trivial operation.
+ EXPECT_TRUE(APFloat(2.0).getExactInverse(&inv));
+ EXPECT_TRUE(inv.bitwiseIsEqual(APFloat(0.5)));
+ EXPECT_TRUE(APFloat(2.0f).getExactInverse(&inv));
+ EXPECT_TRUE(inv.bitwiseIsEqual(APFloat(0.5f)));
+
+ // FLT_MIN
+ EXPECT_TRUE(APFloat(1.17549435e-38f).getExactInverse(&inv));
+ EXPECT_TRUE(inv.bitwiseIsEqual(APFloat(8.5070592e+37f)));
+
+ // Large float
+ EXPECT_TRUE(APFloat(1.7014118e38f).getExactInverse(&inv));
+ EXPECT_TRUE(inv.bitwiseIsEqual(APFloat(5.8774718e-39f)));
+
+ // Zero
+ EXPECT_FALSE(APFloat(0.0).getExactInverse(0));
+ // Denormalized float
+ EXPECT_FALSE(APFloat(1.40129846e-45f).getExactInverse(0));
+}
+
}