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Fix MathUtil.Denormals with clang 15/16 #11485

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merged 2 commits into from
Apr 17, 2023
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Fix MathUtil.Denormals with clang 15/16 #11485

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c65fc9d
Fix MathUtil.Denormals with clang 15/16
daschuer Apr 17, 2023
c9342ec
Add a comment about clang >= 15 behaviour
daschuer Apr 17, 2023
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15 changes: 11 additions & 4 deletions src/test/mathutiltest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -64,19 +64,26 @@ TEST_F(MathUtilTest, Denormal) {
_MM_SET_DENORMALS_ZERO_MODE(_MM_DENORMALS_ZERO_OFF);
_MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_OFF);

volatile float fDenormal = std::numeric_limits<float>::min() / 2.0f;
// Note: The volatile keyword makes sure that the division is executed on the target
// and not by the pre-processor. In case of clang >= 15 the pre-processor flushes to
// zero with -ffast-math enabled.
volatile float fDenormal = std::numeric_limits<float>::min();
fDenormal /= 2.0f;
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Thank you! Please add a comment why the operations are written in this style including the volatile keyword.

EXPECT_NE(0.0f, fDenormal);

volatile double dDenormal = std::numeric_limits<double>::min() / 2.0;
volatile double dDenormal = std::numeric_limits<double>::min();
dDenormal /= 2.0;
EXPECT_NE(0.0, dDenormal);

_MM_SET_DENORMALS_ZERO_MODE(_MM_DENORMALS_ZERO_ON);
_MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_ON);

fDenormal = std::numeric_limits<float>::min() / 2.0f;
fDenormal = std::numeric_limits<float>::min();
fDenormal /= 2.0f;
EXPECT_EQ(0.0f, fDenormal);

dDenormal = std::numeric_limits<double>::min() / 2.0;
dDenormal = std::numeric_limits<double>::min();
dDenormal /= 2.0;
EXPECT_EQ(0.0, dDenormal);

#endif
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