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From: dik@cwi.nl (Dik T. Winter)
Subject: Re: What's the best language to start with? [was: Re: Should I learn
 C or Pascal?]
Date: 1996/08/11
Message-ID: <Dvy5x4.Kwq@cwi.nl>#1/1
X-Deja-AN: 173435528
sender: news@cwi.nl (The Daily Dross)
references: <4udb2o$7io@solutions.solon.com>
 <01bb8569$9910dca0$87ee6fce@timpent.airshields.com>
 <g1sp9xtkmd.fsf@hotspec.lanl.gov>
organization: CWI, Amsterdam
newsgroups: comp.lang.c,comp.lang.c++,comp.unix.programmer,comp.lang.ada
Date: 1996-08-11T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <g1sp9xtkmd.fsf@hotspec.lanl.gov> clodius@hotspec.lanl.gov (William Clodius) writes:
 > There is one special case of recursion, fortunately the most commonly
 > encountered case, where it is "ridiculously" easy for a compiler to
 > see that the recursion can be replaced by iteration.
...
Etc.  An interesting thread, but I wish to add that I know of at least
one system were a recursive algorithm was *significantly faster* than
the equivalent one with tail recursion removed.

But talking about that "gcd" thingy.  I tested and found the following
on two different architectures (times are seconds for a complete program):

		recursive	non-recursive

arch1, non-opt	0.52		0.42
arch1, opt	0.43		0.41

arch2, non-opt	2.65		0.44
arch2, opt	0.39		0.42

Now, what does this prove?  Absolutely nothing (except that there is
something strange with the non-optimization on arch2).  And what are
we talking about anyway?  The call was:
	gcd(2971215073LU, 1836311903LU);
(and if you do not understand why I used those numbers, those are the
absolutely worst case for 32-bit numbers; Fibonacci, you know).
That was the call and it was executed 10,000 times.  So we are talking
about a routine taking some tens of microseconds.  If that would form
a large part of a total program (large enough to make a 10% improvement
worthwhile), I would bother more about the program.

Somebody used the word "microoptimization"; how right he/she was.
-- 
dik t. winter, cwi, kruislaan 413, 1098 sj  amsterdam, nederland, +31205924098
home: bovenover 215, 1025 jn  amsterdam, nederland; http://www.cwi.nl/~dik/