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From: dewar@cs.nyu.edu (Robert Dewar)
Subject: Re: Teaching sorts [was Re: What's the best language to start with?]
Date: 1996/08/24
Message-ID: <dewar.840911509@schonberg>#1/1
X-Deja-AN: 176235069
references: <DwGoHq.6n7@cwi.nl> <01bb8f1b$ce59c820$32ee6fce@timhome2>
 <TANMOY.96Aug21083507@qcd.lanl.gov> <4vfk6b$i6h@krusty.irvine.com>
 <christian.bau-2208961046370001@christian-mac.isltd.insignia.com>
 <1996Aug22.165831.1@eisner> <4vjik9$eao@cnn.Princeton.EDU>
organization: Courant Institute of Mathematical Sciences
newsgroups: comp.lang.c,comp.lang.c++,comp.unix.programmer,comp.lang.ada
Date: 1996-08-24T00:00:00+00:00
List-Id: <comp.lang.ada>


Tim said

"This sort of behavior isn't that rare at all; I've seen it in quite a
number of my benchmarks.  An interesting one I found is that the time
required to memcpy() 34 bytes is 5 times *less* than the time required
to memcpy 30 bytes on my system.  From a graph of time vs n, it
appears that memcpy() switches algorithms at 32 bytes (I believe from
a straightforward copy to something along the lines of Duff's device,
since assymptotically it is very close to my routine using the latter
method).
"


Still you may be simply be seeing cache effects, it is very hard to
control for these.