Merge pull request #202 from Tilka/mathutil

MathUtil: add IntFloat/IntDouble constructors and test FlushToZero()

Source/Core/Common/MathUtil.cpp

@@ -15,8 +15,7 @@ namespace MathUtil
 u32 ClassifyDouble(double dvalue)
 {
 	// TODO: Optimize the below to be as fast as possible.
-	IntDouble value;
-	value.d = dvalue;
+	IntDouble value(dvalue);
 	u64 sign = value.i & DOUBLE_SIGN;
 	u64 exp  = value.i & DOUBLE_EXP;
 	if (exp > DOUBLE_ZERO && exp < DOUBLE_EXP)
@@ -55,8 +54,7 @@ u32 ClassifyDouble(double dvalue)
 u32 ClassifyFloat(float fvalue)
 {
 	// TODO: Optimize the below to be as fast as possible.
-	IntFloat value;
-	value.f = fvalue;
+	IntFloat value(fvalue);
 	u32 sign = value.i & FLOAT_SIGN;
 	u32 exp  = value.i & FLOAT_EXP;
 	if (exp > FLOAT_ZERO && exp < FLOAT_EXP)

Source/Core/Common/MathUtil.h

@@ -36,43 +36,49 @@ static const u32 FLOAT_SIGN = 0x80000000,
 union IntDouble {
 	double d;
 	u64 i;
+
+	explicit IntDouble(u64 _i) : i(_i) {}
+	explicit IntDouble(double _d) : d(_d) {}
 };
 union IntFloat {
 	float f;
 	u32 i;
+
+	explicit IntFloat(u32 _i) : i(_i) {}
+	explicit IntFloat(float _f) : f(_f) {}
 };
 
 inline bool IsINF(double d)
 {
-	IntDouble x; x.d = d;
+	IntDouble x(d);
 	return (x.i & ~DOUBLE_SIGN) == DOUBLE_EXP;
 }
 
 inline bool IsNAN(double d)
 {
-	IntDouble x; x.d = d;
+	IntDouble x(d);
 	return ((x.i & DOUBLE_EXP) == DOUBLE_EXP) &&
 	       ((x.i & DOUBLE_FRAC) != DOUBLE_ZERO);
 }
 
 inline bool IsQNAN(double d)
 {
-	IntDouble x; x.d = d;
+	IntDouble x(d);
 	return ((x.i & DOUBLE_EXP) == DOUBLE_EXP) &&
 	       ((x.i & DOUBLE_QBIT) == DOUBLE_QBIT);
 }
 
 inline bool IsSNAN(double d)
 {
-	IntDouble x; x.d = d;
+	IntDouble x(d);
 	return ((x.i & DOUBLE_EXP) == DOUBLE_EXP) &&
 	       ((x.i & DOUBLE_FRAC) != DOUBLE_ZERO) &&
 	       ((x.i & DOUBLE_QBIT) == DOUBLE_ZERO);
 }
 
 inline float FlushToZero(float f)
 {
-	IntFloat x; x.f = f;
+	IntFloat x(f);
 	if ((x.i & FLOAT_EXP) == 0)
 	{
 		x.i &= FLOAT_SIGN;  // turn into signed zero
@@ -82,7 +88,7 @@ inline float FlushToZero(float f)
 
 inline double FlushToZero(double d)
 {
-	IntDouble x; x.d = d;
+	IntDouble x(d);
 	if ((x.i & DOUBLE_EXP) == 0)
 	{
 		x.i &= DOUBLE_SIGN;  // turn into signed zero

Source/UnitTests/Common/MathUtilTest.cpp

@@ -4,6 +4,7 @@
 
 #include <gtest/gtest.h>
 #include <limits>
+#include <random>
 
 #include "Common/MathUtil.h"
 
@@ -29,7 +30,7 @@ TEST(MathUtil, Clamp)
 
 TEST(MathUtil, IsINF)
 {
-	EXPECT_TRUE(MathUtil::IsINF( std::numeric_limits<double>::infinity()));
+	EXPECT_TRUE(MathUtil::IsINF(+std::numeric_limits<double>::infinity()));
 	EXPECT_TRUE(MathUtil::IsINF(-std::numeric_limits<double>::infinity()));
 }
 
@@ -63,3 +64,43 @@ TEST(MathUtil, Log2)
 	EXPECT_EQ(3, Log2(15));
 	EXPECT_EQ(63, Log2(0xFFFFFFFFFFFFFFFFull));
 }
+
+TEST(MathUtil, FlushToZero)
+{
+	// To test the software implementation we need to make sure FTZ and DAZ are disabled.
+	// Using volatile here to ensure the compiler doesn't constant-fold it,
+	// we want the multiplication to occur at test runtime.
+	volatile float s = std::numeric_limits<float>::denorm_min();
+	volatile double d = std::numeric_limits<double>::denorm_min();
+	EXPECT_LT(0, s * 2);
+	EXPECT_LT(0, d * 2);
+
+	EXPECT_EQ(+0, MathUtil::FlushToZero(+std::numeric_limits<double>::denorm_min()));
+	EXPECT_EQ(-0, MathUtil::FlushToZero(-std::numeric_limits<double>::denorm_min()));
+	EXPECT_EQ(+0, MathUtil::FlushToZero(+std::numeric_limits<double>::min() / 2));
+	EXPECT_EQ(-0, MathUtil::FlushToZero(-std::numeric_limits<double>::min() / 2));
+	EXPECT_EQ(std::numeric_limits<double>::min(), MathUtil::FlushToZero(std::numeric_limits<double>::min()));
+	EXPECT_EQ(std::numeric_limits<double>::max(), MathUtil::FlushToZero(std::numeric_limits<double>::max()));
+	EXPECT_EQ(+std::numeric_limits<double>::infinity(), MathUtil::FlushToZero(+std::numeric_limits<double>::infinity()));
+	EXPECT_EQ(-std::numeric_limits<double>::infinity(), MathUtil::FlushToZero(-std::numeric_limits<double>::infinity()));
+
+	// Test all subnormals as well as an equally large set of random normal floats.
+	std::default_random_engine engine(0);
+	std::uniform_int_distribution<u32> dist(0x00800000u, 0x7fffffffu);
+	for (u32 i = 0; i <= 0x007fffffu; ++i)
+	{
+		MathUtil::IntFloat x(i);
+		EXPECT_EQ(+0, MathUtil::FlushToZero(x.f));
+
+		x.i = i | 0x80000000u;
+		EXPECT_EQ(-0, MathUtil::FlushToZero(x.f));
+
+		x.i = dist(engine);
+		MathUtil::IntFloat y(MathUtil::FlushToZero(x.f));
+		EXPECT_EQ(x.i, y.i);
+
+		x.i |= 0x80000000u;
+		y.f = MathUtil::FlushToZero(x.f);
+		EXPECT_EQ(x.i, y.i);
+	}
+}