expm1 for GNU gfortran

Question

Is there any way to call a fast implementation of expm1 from GNU Fortran? Ideally, it would be great to have a function to calculate (exp(x)-1)/x directly to avoid extra check for zero argument. Elemental version of expm1 would be especially helpful.

Answer 1

This is how it's called from libm:

  use, intrinsic :: iso_c_binding, only: c_double

  implicit none

  interface
     real(c_double) function expm1(x) bind(c, name='expm1')
       import c_double
       real(c_double), intent(in), value :: x
     end function expm1
  end interface

  print*, expm1(3.4d0)

end program

If the glibc source code for the function does not look too discouraging then you might wish to translate it into Fortran in order to make it elemental (if by elemental you meant the Fortran keyword).