trying to speed up a  f90 program I was thinking about the difference
if I put my subroutines in a module or if I define an interface. Will
there be any differences in speed for these two approaches ?

Thanks for your help in advance !

Except for the speed of development. Writing interface bodies is
error-prone and thus likely to slow down code development.

Well, ok, that is certainly an overgeneralization, as some are likely to
point out. But I felt I should say more than the one-word answer "no". I
can't really think of any useful elaboration on that other than that it
isn't likely to be a constructive avenue to pursue.

About the closest thing I can think of is the issue of copy-in/copy-out
for array arguments. That doesn't have anything directly to do with
using modules versus interface bodies. But it is at least vaguely
related to the subject of explicit interfaces.

thanks for your quick response !
So I will not waste any time for changing from interfaces to a module.

Cheers,

The advantage is that changes to the interface of these
routines are automatically known to the compiler.

If you have interface blocks in the calling routines, there
will still be a possibility for mismatches.

Consider:

subroutine suba( x )
    real :: x
    ...
end subroutine

and:

program test_suba
    interface
        subroutine suba( x, y )
            real :: x, y
        end subroutine
    end interface

    call suba( x, y )
end program

There is no "intrinsic" relationship between the
implementation of the routine and the interface block.

If however:

module moda
contains
subroutine suba( x )
    real :: x
    ...
end subroutine
end module

and:

program test_suba
    use moda

    call suba( x, y )
end program

the compiler can "see" the mismatch.

It is up to you, but I think modules are preferrable.

Regards,

thanks for your explanations ! They help to improve my knowledge of
Fortran.

Regards,