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From: dbrown@vigra.com (David Brown)
Subject: Re: CRC in Ada?
Date: 1997/03/07
Message-ID: <oslo7zybrt.fsf@ted.vigra.com>#1/1
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Sender: dbrown@ted.vigra.com
References: <1997Mar2.220652@nova.wright.edu> <oslo83b70l.fsf@ted.vigra.com>
Organization: VisiCom Laboratories, Inc.
Newsgroups: comp.lang.ada
Date: 1997-03-07T00:00:00+00:00
List-Id: <comp.lang.ada>


ohk@edeber.tfdt-o.nta.no (Ole-Hjalmar Kristensen FOU.TD/DELAB) writes:

> char buf[4096];
> 
> main() {
>    int c,n,total=0;
>    while ((n = read(0,buf,sizeof(buf))) > 0) {
>       int i;
>       for (i = 0; i < n; i++) {
>          c = buf[i];
>          total++;
>       }
>    }
>    printf("total %d\n",total);
> }
> 
> Average results obtained with time:
> 0.12u 0.29s 0:00.41 100.0%
> 
> It is somewhat surprising that the difference between the user CPU
> times is so large, but I'm more surprised by the speed of the second
> version than by the slowness of the first.

I suspect that most of the inner loop is being optimized out.  Since
you don't actually do anything with 'c', it probably is never actually
used.  The buffer is probably never accessed.  A slightly better test
would be to compute a simple checksum or something.

Dave Brown
dbrown@vigra.com