Commit 8dca9f97 authored by Gael Guennebaud's avatar Gael Guennebaud
Browse files

Add numext::sqrt function to enable custom optimized implementation. 

This changeset add two specializations for float/double on SSE. Those
are mostly usefull with GCC for which std::sqrt add an extra and costly
check on the result of _mm_sqrt_*. Clang does not add this burden.

In this changeset, only DenseBase::norm() makes use of it.
parent 34340458

Eigen/src/Core/Dot.h

+1 −2
Original line number Diff line number Diff line
@@ -99,8 +99,7 @@ EIGEN_STRONG_INLINE typename NumTraits<typename internal::traits<Derived>::Scala 
template<typename Derived>

inline typename NumTraits<typename internal::traits<Derived>::Scalar>::Real MatrixBase<Derived>::norm() const

{

  EIGEN_USING_STD_MATH(sqrt)

  return sqrt(squaredNorm());

  return numext::sqrt(squaredNorm());

}



/** \returns an expression of the quotient of *this by its own norm.

Eigen/src/Core/MathFunctions.h

+18 −2
Original line number Diff line number Diff line
@@ -954,8 +954,8 @@ T (ceil)(const T& x) 
  return ceil(x);

}



// Log base 2 for 32 bits positive integers.

// Conveniently returns 0 for x==0.

/** Log base 2 for 32 bits positive integers.

  * Conveniently returns 0 for x==0. */

inline int log2(int x)

{

  eigen_assert(x>=0);
@@ -969,6 +969,22 @@ inline int log2(int x) 
  return table[(v * 0x07C4ACDDU) >> 27];

}



/** \returns the square root of \a x.

  *

  * It is essentially equivalent to \code using std::sqrt; return sqrt(x); \endcode,

  * but slightly faster for float/double and some compilers (e.g., gcc), thanks to

  * specializations when SSE is enabled.

  *

  * It's usage is justified in performance critical functions, like norm/normalize.

  */

template<typename T>

EIGEN_DEVICE_FUNC EIGEN_ALWAYS_INLINE

T sqrt(const T &x)

{

  EIGEN_USING_STD_MATH(sqrt);

  return sqrt(x);

}



} // end namespace numext



namespace internal {

Eigen/src/Core/arch/SSE/MathFunctions.h

+22 −0
Original line number Diff line number Diff line
@@ -518,6 +518,28 @@ Packet2d prsqrt<Packet2d>(const Packet2d& x) { 


} // end namespace internal



namespace numext {



template<>

EIGEN_DEVICE_FUNC EIGEN_ALWAYS_INLINE

float sqrt(const float &x)

{

  return internal::pfirst(_mm_sqrt_ss(_mm_set_ss(x)));

}



template<>

EIGEN_DEVICE_FUNC EIGEN_ALWAYS_INLINE

double sqrt(const double &x)

{

#if EIGEN_COMP_GNUC

  return internal::pfirst(__builtin_ia32_sqrtsd(_mm_set_sd(x)));

#else

  return internal::pfirst(_mm_sqrt_pd(_mm_set_sd(x)));

#endif

}



} // end namespace numex



} // end namespace Eigen



#endif // EIGEN_MATH_FUNCTIONS_SSE_H