I have the following code to calculate a checksum (the checksum algoritm is not under my control):
open my $fh, "<", "myfile" or die;
my $check_value = 0;
while (1) {
my $buf;
my $cnt = read $fh, $buf, 4;
if (!defined $cnt) {
die("Error while reading from input file: $!");
} elsif ($cnt==0) {
last;
} elsif ($cnt%4) {
die("File or chunk does not seem to have a length that's a multi
+ple of 4 bytes");
}
my $val = unpack("L",$buf);
$check_value ^= $val;
my $rotate = $check_value & 0x80000000;
$check_value = ($check_value << 1 ) & 0xffffffff;
if ($rotate) { $check_value |= 0x01; }
}
It works but is terribly slow. Any suggestions to speed it up?. This looks like the kind of thing that would be a lot faster in C, and trivially so in assembler because of the nice rotate instructions; I'd rather avoid shelling out to a subprocess just for this though.
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