Re: Ada vs Fortran for scientific applications

[glen herrmannsfeldt <gah@ugcs.caltech.edu>]

Jan Vorbr�ggen wrote:
>> OK, but say for a certain program it is more efficient to store a 
>> complex array with all the real parts followed by all the imaginary 
>> parts, and the compiler figured this out.  The "as if" rule would work 
>> only if there was no other way for the program/programmer to discover 
>> the change.  If the array was in COMMON, EQUIVALENCEd, or passed to an 
>> external routine, this optimization most likely couldn't be done.
>> Without any legal way to view the storage association, it would seem 
>> possible to do it.

> Precisely what I was thinking. So historic baggage is weighing Fortran down
> in this particular case.

It seems pretty convenient for FFT routines to treat a COMPLEX array as 
REAL.  It would take some time to know if this speeds up the FFT or not.

One alternative, as you say precluded by Fortran history, would be 
something like the descriptor of assumed shape arrays that could 
describe a COMPLEX type where the real and imaginary parts are not 
consecutive.  It would seem that this could be done in the case of 
assumed shape arrays, as they are already incompatible with assumed size 
arrays, normally requiring a copy if passed to an assumed size array 
subprogram.

-- glen