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From: hrubin@osupyr.UUCP
Newsgroups: comp.lang.c
Subject: Re: Portable C vs Efficient C or "Cost of Portability"
Message-ID: <170@osupyr.UUCP>
Date: Sat, 4-Apr-87 11:04:17 EST
Article-I.D.: osupyr.170
Posted: Sat Apr  4 11:04:17 1987
Date-Received: Wed, 8-Apr-87 03:01:47 EST
References: <213@pyuxe.UUCP> <1024@epimass.UUCP>
Organization: Department of Statistics
Lines: 29
Keywords: portability, performance
Summary: I rarely find portability for efficient code

I frequently find that reasonably good code can be portable, but rarely do I
find efficient code portable.  In fact, rarely do I find C code (or any other
HLL) to be efficient.  Assuming that the compiler allows you to put all the
variables (but not, of course, the arrays)in registers, the following fragment
of code is better on VAXen

	t = *(m++) ^ *(h++);
	*(k++) = t;
	*(z++) ^= t;

than

	t = m[x] ^ h[x];
	k[x] = t;
	z[x] ^= t;
	x++;

while on the pyramid the reverse is true.  This is because of the computer
architecture.  When operations not supported by C are needed, clearly the
problem is worse. 
-- 
Herman Rubin
Until mid May:
Department of Statistics, Cockins Hall, 1958 Neil Avenue
Ohio State University, Columbus OH43210
hrubin@osupyr or cbosgd!osu-eddie!osupyr!hrubin or ts0474@ohstvma.bitnet
"Permanent":
Department of Statistics, Purdue University, West Lafayette IN47907
hrubin@l.cc.purdue.edu or ihnp4!pur-ee!stat-l!hrubin or hrubin@purccvm.bitnet