0.9.5/api/a00030_source.html

 #ifndef GLM_GTX_fast_square_root

 #define GLM_GTX_fast_square_root


 // Dependency:

 #include "../glm.hpp"


 #if(defined(GLM_MESSAGES) && !defined(GLM_EXT_INCLUDED))

 #       pragma message("GLM: GLM_GTX_fast_square_root extension included")

 #endif


 namespace glm

 {


         template <typename genType>

         genType fastSqrt(genType const & x);


         template <typename genType>

         genType fastInverseSqrt(genType const & x);


         template <typename genType>

         typename genType::value_type fastLength(genType const & x);


         template <typename genType>

         typename genType::value_type fastDistance(genType const & x, genType const & y);


         template <typename genType>

         genType fastNormalize(genType const & x);


 }// namespace glm


 #include "fast_square_root.inl"


 #endif//GLM_GTX_fast_square_root

glm::fastSqrt
genType fastSqrt(genType const &x)
Faster than the common sqrt function but less accurate.

glm::fastInverseSqrt
genType fastInverseSqrt(genType const &x)
Faster than the common inversesqrt function but less accurate.

glm::fastDistance
genType::value_type fastDistance(genType const &x, genType const &y)
Faster than the common distance function but less accurate.

glm::fastNormalize
genType fastNormalize(genType const &x)
Faster than the common normalize function but less accurate.

glm::fastLength
genType::value_type fastLength(genType const &x)
Faster than the common length function but less accurate.