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From: blu@millipore.com (Brian Utterback)
Newsgroups: comp.lang.perl
Subject: PERL Novice needs help.
Message-ID: <1991Jan7.205909.674@millipore.com>
Date: 7 Jan 91 20:59:09 GMT
Organization: Millipore Corporation
Lines: 31

Okay perl hackers, I need your help.  I have oft'times seen it written that
if you are iterating over a variable you are probably doing it wrong in perl.
So, I need an alternate approach since the one I thought of is abysmally 
slow.

I am processing some raw grey-scale image, 8 bits per value.  There are 
X scanlines of Y pixels each.  What I want is to tally the values into
a histogram and produce the hex dump of the values, but with the image scaled
down to a third it's original size. So in loose perl I have the following:

for (x=0;x<X;x++){
	sysread(FILE,$scanline,Y);
	$scanvalues = unpack("C$Y",$scanline);
	for (y=0;y<Y;y++) {
		@histogram[$scanvalue[$y]]++;
		if ((0 == $x%3) && (0 == $y%3)) {
			if ($scanvalue[$y] < 16) {print "0";}
			printf("%x",$scanvalue[$y]);
		}
	}
	if (0 == $x%3) {print "\n";}
}

I know, really ugly huh?  Only thing is, how do I speed it up?  Oh, by the way,
each value needs to be exactly 2 hex digits.

-- 
Brian Utterback, Millipore Corporation, 75G Wiggins Ave., Bedford Ma. 01730
Work:617-275-9200x8245, Home:603-891-2536
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