General Fortran Questions

[frank_m1]

Which is faster, in place operations or not in place operations?
e.x.

c = a + b

or

a = a + b

How would I use Allocateso thatthe address of the first element of an arrayis divisible in bytes by 16, 32 or 64?

[Steven_L_Intel1 · Accepted solution]

Your first question does not have a simple answer, other than "It depends". My advice is to write the code that is clearest to you and let the compiler worry about optimization. If you're talking scalars, I doubt you could ever detect a difference between these - with arrays, you might get into memory bandwidth issues with a separate target.

You can request alignment of allocatable variables by adding the directive:

!DEC$ ATTRIBUTES ALIGN:16 :: varname

replace 16 by 32 or 64 or whatever reasonable power of 2 you want. See the documentation on this directive for more details.

[frank_m1]

Thank you.