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From: Jacob Sparre Andersen <sparre@nbi.dk>
Newsgroups: comp.lang.ada
Subject: Re: What is faster Ada or C?
Date: Fri, 07 Dec 2001 18:03:33 +0100
Organization: Centre for Chaos and Turbulence Studies, Niels Bohr Institute
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Date: 2001-12-07T18:03:33+01:00
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Preben Randhol wrote:

> On 07 Dec 2001 17:16:18 +0200, Aaro Koskinen wrote:
> > Jacob Sparre Andersen <sparre@nbi.dk> writes:
> >>  * Why are the two programs below not equivalent?
> >>  * How can I get the Ada program to run as fast as the C++ program?
> > [..]
> >> Compilation...: gnatmake sqrt_timer -O3 -gnatn
> > [..]
> >>    for i in 1 .. 10_000_000 loop
> >>       X := Sqrt (1.0 + X);
> >>    end loop;
> >
> > Did you try with -gnatp?

I have tried both "-gnatp", "-funroll-loops" and other flags
without any significant change in the timing results.

> I tried to add the -gnatp switch. I compiled the Ada programs twice with
> the -O3 and -S switches. Whether I add the -gnatp switch or not I get
> the exact same assambler source. Is this correct?

That's very likely. There is no need for range checks on the
counter, and I seem to remember that the floating point
operations (in x86 processors) can check for exceptions
without extra code.

> I think the difference between the Ada and C++ program is the Sqrt
> function.

Certainly. (On ix86 processors) GNU C++ inlines the sqrt
operation built into the processor, while GNU Ada makes
calls to a Sqrt function.

> I simplified the two programs by removing sqrt (and using Float in Ada)
> and then both programs run at the same speed, 66ms.

Of course. Then there is no function call to inline.

Jacob
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