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From: "Tim Behrendsen" <tim@airshields.com>
Subject: Re: What's the best language to start with? [was: Re: Should I learn
 C or Pascal?]
Date: 1996/08/13
Message-ID: <01bb88d6$fe8aaaa0$32ee6fce@timhome2>#1/1
X-Deja-AN: 174039891
references: <31FBC584.4188@ivic.qc.ca>
 <01bb8534$b2718bc0$87ee6fce@timpent.airshields.com>
 <danpop.839594575@news.cern.ch>
 <01bb87cf$97ae8e80$87ee6fce@timpent.airshields.com>
 <4unn8o$rkl@solutions.solon.com>
content-type: text/plain; charset=ISO-8859-1
organization: A-SIS
mime-version: 1.0
newsgroups: comp.lang.c,comp.lang.c++,comp.unix.programmer,comp.lang.ada
Date: 1996-08-13T00:00:00+00:00
List-Id: <comp.lang.ada>


Peter Seebach <seebs@solutions.solon.com> wrote in article
<4unn8o$rkl@solutions.solon.com>...
> In article <01bb87cf$97ae8e80$87ee6fce@timpent.airshields.com>,
> Tim Behrendsen <tim@airshields.com> wrote:
> >> >int a[50000],b[50000],c[50000],d[50000],e[50000];
> 
> >> >void test1()
> >> >{
> >> >    int i, j;
> >> >    for (j = 0; j < 10; ++j) {
> >> >        for (i = 0; i < 50000; ++i) {
> >> >            ++a[i]; ++b[i]; ++c[i]; ++d[i]; ++e[i];
> >> >        }
> >> >    }
> >> >}
> 
> >> >void test2()
> >> >{
> >> >    int i, j;
> >> >    for (j = 0; j < 10; ++j) {
> >> >        for (i = 0; i < 50000; ++i) ++a[i];
> >> >        for (i = 0; i < 50000; ++i) ++b[i];
> >> >        for (i = 0; i < 50000; ++i) ++c[i];
> >> >        for (i = 0; i < 50000; ++i) ++d[i];
> >> >        for (i = 0; i < 50000; ++i) ++e[i];
> >> >    }
> >> >}
> 
> >Show me the computer where test1 comes out faster.
> 
> gcc/SPARC, with *NO* optimization.  test1 runs 10 times in 15.66 seconds,
> test2 takes 22.02 seconds.
> 
> With optimization, test2 comes out faster on that compiler.
> 
> In other words, which is faster depends on the compiler.  And on context.
>
> >Not gonna find this mythical bizarre beast, except for trivial
> >differences because of the extra loop overhead.
> 
> Trivial, like a factor of 50%.

I suspect that no optimization is not using pointers/registers.
Try rewriting the subroutines to use pointers both ways and then
try it with no optimization.

> >Again, is it the case that I can order my code into any
> >algorithmically valid sequence and get identical running times?
> 
> No.  However, it is the case that the differences simply don't justify
the
> overhead.  I see the "faster" version as having more code, and no real
reason
> for it.  The pithy 10% advantage it has when it's better does not justify
the
> 50% disadvantage it has when it's worse.  On my systems.

Only 10% on SPARC?  Crummy paging architecture.

-- Tim Behrendsen (tim@airshields.com)