CL for perf tryjob

Source/wtf/MathExtras.h

Index: Source/wtf/MathExtras.h
diff --git a/Source/wtf/MathExtras.h b/Source/wtf/MathExtras.h
index 5925ca5e89a1d96dfb6fa34b9908ce9d10ee32f2..808ff9050d0774a024d8510d8e6e3f3cecf335e6 100644
--- a/Source/wtf/MathExtras.h
+++ b/Source/wtf/MathExtras.h
@@ -26,12 +26,13 @@
 #ifndef WTF_MathExtras_h
 #define WTF_MathExtras_h
 
+#include "wtf/Assertions.h"
 #include "wtf/CPU.h"
+#include <algorithm>
 #include <cmath>
 #include <limits>
 
 #if COMPILER(MSVC)
-#include "wtf/Assertions.h"
 #include <stdint.h>
 #endif
 
@@ -222,54 +223,147 @@ inline float grad2rad(float g) { return g * piFloat / 200.0f; }
 inline float turn2grad(float t) { return t * 400; }
 inline float grad2turn(float g) { return g / 400; }
 
-// std::numeric_limits<T>::min() returns the smallest positive value for floating point types
-template<typename T> inline T defaultMinimumForClamp() { return std::numeric_limits<T>::min(); }
-template<> inline float defaultMinimumForClamp() { return -std::numeric_limits<float>::max(); }
-template<> inline double defaultMinimumForClamp() { return -std::numeric_limits<double>::max(); }
-template<typename T> inline T defaultMaximumForClamp() { return std::numeric_limits<T>::max(); }
+// clampTo() is implemented by templated helper classes (to allow for partial
+// template specialization) as well as several helper functions.
 
-template<typename T> inline T clampTo(double value, T min = defaultMinimumForClamp<T>(), T max = defaultMaximumForClamp<T>())
+// This helper function can be called when we know that:
+// (1) The type signednesses match so the compiler will not produce signed vs.
+//     unsigned warnings
+// (2) The default type promotions/conversions are sufficient to handle things
+//     correctly
+template<typename LimitType, typename ValueType> inline LimitType clampToDirectComparison(ValueType value, LimitType min, LimitType max)
 {
-    if (value >= static_cast<double>(max))
+    if (value >= max)
         return max;
-    if (value <= static_cast<double>(min))
-        return min;
-    return static_cast<T>(value);
+    return (value <= min) ? min : static_cast<LimitType>(value);
 }
-template<> inline long long int clampTo(double, long long int, long long int); // clampTo does not support long long ints.
 
-inline int clampToInteger(double value)
-{
-    return clampTo<int>(value);
-}
-
-inline unsigned clampToUnsigned(double value)
-{
-    return clampTo<unsigned>(value);
-}
-
-inline float clampToFloat(double value)
-{
-    return clampTo<float>(value);
-}
-
-inline int clampToPositiveInteger(double value)
-{
-    return clampTo<int>(value, 0);
-}
+// For any floating-point limits, or integral limits smaller than long long, we
+// can cast the limits to double without losing precision; then the only cases
+// where |value| can't be represented accurately as a double are the ones where
+// it's outside the limit range anyway.  So doing all comparisons as doubles
+// will give correct results.
+//
+// In some cases, we can get better performance by using
+// clampToDirectComparison().  We use a templated class to switch between these
+// two cases (instead of simply using a conditional within one function) in
+// order to only compile the clampToDirectComparison() code for cases where it
+// will actually be used; this prevents the compiler from emitting warnings
+// about unsafe code (even though we wouldn't actually be executing that code).
+template<bool canUseDirectComparison, typename LimitType, typename ValueType> class ClampToNonLongLongHelper;
+template<typename LimitType, typename ValueType> class ClampToNonLongLongHelper<true, LimitType, ValueType> {
+public:
+    static inline LimitType clampTo(ValueType value, LimitType min, LimitType max)
+    {
+        return clampToDirectComparison(value, min, max);
+    }
+};
+
+template<typename LimitType, typename ValueType> class ClampToNonLongLongHelper<false, LimitType, ValueType> {
+public:
+    static inline LimitType clampTo(ValueType value, LimitType min, LimitType max)
+    {
+        const double doubleValue = static_cast<double>(value);
+        if (doubleValue >= static_cast<double>(max))
+            return max;
+        if (doubleValue <= static_cast<double>(min))
+            return min;
+        // If the limit type is integer, we might get better performance by
+        // casting |value| (as opposed to |doubleValue|) to the limit type.
+        return std::numeric_limits<LimitType>::is_integer ? static_cast<LimitType>(value) : static_cast<LimitType>(doubleValue);
+    }
+};
+
+// The unspecialized version of this templated class handles clamping to
+// anything other than [unsigned] long long int limits.  It simply uses the
+// class above to toggle between the "fast" and "safe" clamp implementations.
+template<typename LimitType, typename ValueType> class ClampToHelper {
+public:
+    static inline LimitType clampTo(ValueType value, LimitType min, LimitType max)
+    {
+        // We only use clampToDirectComparison() when the integerness and
+        // signedness of the two types matches.
+        //
+        // If the integerness of the types doesn't match, then at best
+        // clampToDirectComparison() won't be much more efficient than the
+        // cast-everything-to-double method, since we'll need to convert to
+        // floating point anyway; at worst, we risk incorrect results when
+        // clamping a float to a 32-bit integral type due to potential precision
+        // loss.
+        //
+        // If the signedness doesn't match, clampToDirectComparison() will
+        // produce warnings about comparing signed vs. unsigned, which are apt
+        // since negative signed values will be converted to large unsigned ones
+        // and we'll get incorrect results.
+        return ClampToNonLongLongHelper<std::numeric_limits<LimitType>::is_integer == std::numeric_limits<ValueType>::is_integer && std::numeric_limits<LimitType>::is_signed == std::numeric_limits<ValueType>::is_signed, LimitType, ValueType>::clampTo(value, min, max);
+    }
+};
+
+// Clamping to [unsigned] long long int limits requires more care.  These may
+// not be accurately representable as doubles, so instead we cast |value| to the
+// limit type.  But that cast is undefined if |value| is floating point and
+// outside the representable range of the limit type, so we also have to check
+// for that case explicitly.
+template<typename ValueType> class ClampToHelper<long long int, ValueType> {
+public:
+    static inline long long int clampTo(ValueType value, long long int min, long long int max)
+    {
+        if (!std::numeric_limits<ValueType>::is_integer) {
+            if (value > 0) {
+                if (static_cast<double>(value) >= static_cast<double>(std::numeric_limits<long long int>::max()))
+                    return max;
+            } else if (static_cast<double>(value) <= static_cast<double>(std::numeric_limits<long long int>::min())) {
+                return min;
+            }
+        }
+        // Note: If |value| were unsigned long long int, it could be larger than
+        // the largest long long int, and this code would be wrong; we handle
+        // this case with a separate full specialization below.
+        return clampToDirectComparison(static_cast<long long int>(value), min, max);
+    }
+};
+
+// This specialization handles the case where the above partial specialization
+// would be potentially incorrect.
+template<> class ClampToHelper<long long int, unsigned long long int> {
+public:
+    static inline long long int clampTo(unsigned long long int value, long long int min, long long int max)
+    {
+        if (max <= 0 || value >= static_cast<unsigned long long int>(max))
+            return max;
+        const long long int longLongValue = static_cast<long long int>(value);
+        return (longLongValue <= min) ? min : longLongValue;
+    }
+};
+
+// This is similar to the partial specialization that clamps to long long int,
+// but because the lower-bound check is done for integer value types as well, we
+// don't need a <unsigned long long int, long long int> full specialization.
+template<typename ValueType> class ClampToHelper<unsigned long long int, ValueType> {
+public:
+    static inline unsigned long long int clampTo(ValueType value, unsigned long long int min, unsigned long long int max)
+    {
+        if (value <= 0)
+            return min;
+        if (!std::numeric_limits<ValueType>::is_integer) {
+            if (static_cast<double>(value) >= static_cast<double>(std::numeric_limits<unsigned long long int>::max()))
+                return max;
+        }
+        return clampToDirectComparison(static_cast<unsigned long long int>(value), min, max);
+    }
+};
 
-inline int clampToInteger(float value)
-{
-    return clampTo<int>(value);
-}
+// This basically reimplements C++11's std::numeric_limits<T>::lowest().
+template<typename T> inline T defaultMinimumForClamp() { return std::numeric_limits<T>::min(); }
+template<> inline float defaultMinimumForClamp<float>() { return -std::numeric_limits<float>::max(); }
+template<> inline double defaultMinimumForClamp<double>() { return -std::numeric_limits<double>::max(); }
 
-inline int clampToInteger(unsigned x)
+// And, finally, the actual function for people to call.
+template<typename LimitType, typename ValueType> inline LimitType clampTo(ValueType value, LimitType min = defaultMinimumForClamp<LimitType>(), LimitType max = std::numeric_limits<LimitType>::max())
 {
-    const unsigned intMax = static_cast<unsigned>(std::numeric_limits<int>::max());
-
-    if (x >= intMax)
-        return std::numeric_limits<int>::max();
-    return static_cast<int>(x);
+    ASSERT(!std::isnan(static_cast<double>(value)));
+    ASSERT(min <= max); // This also ensures |min| and |max| aren't NaN.
+    return ClampToHelper<LimitType, ValueType>::clampTo(value, min, max);
 }
 
 inline bool isWithinIntRange(float x)