This one runs about 10-15 times faster on my system. Toggle $useVec to
alternate between your old version and the one that uses vec(). Please
not that vec() is big-endian. I verified that the output of both
versions are identical.
Hope that helps
Tobias
use strict;
use warnings;
my $header;
my $header_size=8*1024;
my $body;
my $body_size=2048*2048*2;
my $image=$ARGV[0];
open(FH, "+<$image") or die "\nCan not open $image for updating: $!\n";
read(FH, $header, $header_size) == $header_size or print "\nshort read:
$!\n";
read(FH, $body, $body_size) == $body_size or print "\nshort read: $!\n";
my $useVec=1;
if($useVec) {
my $changed=0;
for my $i (0 .. $body_size/2) {
next unless (vec($body,$i,16)>>8 & 1);
$changed++;
vec($body,$i,16) = 1<<8;
}
if($changed) {
seek FH, 0, 0;
print FH $header, $body;
close(FH);
}
} else {
my $body_new;
my $p;
foreach $p (unpack("S*",$body)) {
if ($p&1) {$p=1};
$body_new=$body_new.pack("S",$p); # packing is slow ~40 seconds
}
seek FH, 0, 0;
print FH $header, $body_new;
close(FH);
}
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Bharucha, Nikhil
Sent: Tuesday, March 13, 2007 2:54 PM
To: Su, Yu (Eugene); [email protected]
Subject: RE: how to make it to run faster
I believe the pack function is implemented in C so I don't know how much
faster you can write it...
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