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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: fast computing with GNAT (?)
Date: 2000/04/07
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In article <8ck2ur$sgu$1@news.uit.no>,
  Reinert.Korsnes@npolar.no wrote:
> Hi,
>
> I am comparing GNAT and g77 on linux (RedHat 6.1).
>
> Is it possible to use GNAT in "fast-math mode" similar
> to using g77 like this:
>
> g77 -c -O -ffast-math -malign-double test1.f

A difference like this can be the result of many things, so
careful analysis is needed.

-malign-double can make a huge difference, but is gcc only,
since it violates the standard ABI rules.

Checks can often make a difference

-O4 is too high, we usually find that -O2 is fastest

The trig functions definitely do more in Ada than in Fortran
in terms of error checking and required accuracy. Try simply
importing the Fortran routines if you are satisfied with the
accuracy and lack of error checking in these routines.


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