Xref: news2.mv.net comp.os.msdos.djgpp:5190
From: Joern Sierwald <Sierwald AT tu-harburg DOT d400 DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Speed optimization: memcpy() or for loop ??  ** Some actual test results **
Date: Thu, 20 Jun 1996 10:24:17 +0200
Organization: Technische Universitaet Hamburg-harburg
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Richard Young wrote:
> 
> > Richard Young wrote:
> > > A question for the optimization experts:
> > > For moving data, is it faster to use
> > >
> > > a) memcpy(x,y,n*sizeof(x[0]))
> > > or
> > > b) for (i = 0; i < n; i++) x[i] = y[i];
> > >
> > > or are they basically the same speed.
> 
> Well, I wrote a test program to test several data move options:
> 
> 1) memcpy()
> 2) an index based for loop
> 3) a ptr based for loop
> 
> The results are:  NO DIFFERENCE.
> 
> On my 120 MHz DEC Pentium executing a data move of 100000 floats 2000 times
> took roughly 45 seconds for all options.
> 
> I'm a little surprised that memcpy() wasn't faster.  Am I getting an inlined
> "C" version instead of an assembly coded library function.
> 
 
Not surprising. You're measuring the memory speed of your 
computer. The copy loop is in the 1 Level Cache. In the days of
the 80286 (no Cache) a movsw was faster than a loop. Now it doesn't
matter.

Joern
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