Math: added sqrtInverted() function.

There are SIMD instructions for that, so why not have it in place.

src/Math/Functions.h

@@ -197,7 +197,11 @@ template<std::size_t size, class T> Vector<size, T> abs(const Vector<size, T>& a
 }
 #endif
 
-/** @brief Square root */
+/**
+@brief Square root
+
+@see sqrtInverted(), Vector::length()
+*/
 #ifdef DOXYGEN_GENERATING_OUTPUT
 template<class T> inline T sqrt(const T& a);
 #else
@@ -212,6 +216,25 @@ template<std::size_t size, class T> Vector<size, T> sqrt(const Vector<size, T>&
 }
 #endif
 
+/**
+@brief Inverse square root
+
+@see sqrt()
+*/
+#ifdef DOXYGEN_GENERATING_OUTPUT
+template<class T> inline T sqrtInverted(const T& a);
+#else
+template<class T> inline typename std::enable_if<std::is_arithmetic<T>::value, T>::type sqrtInverted(T a) {
+    return T(1)/std::sqrt(a);
+}
+template<std::size_t size, class T> Vector<size, T> sqrtInverted(const Vector<size, T>& a) {
+    Vector<size, T> out;
+    for(std::size_t i = 0; i != size; ++i)
+        out[i] = T(1)/std::sqrt(a[i]);
+    return out;
+}
+#endif
+
 /**
 @brief Clamp value
 

src/Math/Test/FunctionsTest.cpp

@@ -38,6 +38,7 @@ class FunctionsTest: public Corrade::TestSuite::Tester {
         void sign();
         void abs();
         void sqrt();
+        void sqrtInverted();
         void clamp();
         void lerp();
         void normalizeUnsigned();
@@ -70,6 +71,7 @@ FunctionsTest::FunctionsTest() {
               &FunctionsTest::sign,
               &FunctionsTest::abs,
               &FunctionsTest::sqrt,
+              &FunctionsTest::sqrtInverted,
               &FunctionsTest::clamp,
               &FunctionsTest::lerp,
               &FunctionsTest::normalizeUnsigned,
@@ -116,6 +118,11 @@ void FunctionsTest::sqrt() {
     CORRADE_COMPARE(Math::sqrt(Vector3i(256, 1, 0)), Vector3i(16, 1, 0));
 }
 
+void FunctionsTest::sqrtInverted() {
+    CORRADE_COMPARE(Math::sqrtInverted(16.0f), 0.25f);
+    CORRADE_COMPARE(Math::sqrtInverted(Vector3(1.0f, 4.0f, 16.0f)), Vector3(1.0f, 0.5f, 0.25f));
+}
+
 void FunctionsTest::clamp() {
     CORRADE_COMPARE(Math::clamp(0.5f, -1.0f, 5.0f), 0.5f);
     CORRADE_COMPARE(Math::clamp(-1.6f, -1.0f, 5.0f), -1.0f);