Re^4: CRC of a string

Ok, I did not know that there exist different versions of how to compute a CRC32. But unfortunately I need this specific one.

Thank you very much for the hint with the Math::BigInt. Now I could get rid of the warnings.

Here the new code:

#!/usr/bin/perl

use strict;
use warnings;

use Math::BigInt;

# solution: 990644297
my $buffer = "/etc/test2.sh";
my $crc = Math::BigInt->new('0');

&determineCrc32($buffer, $crc);

print $crc . "\n";

sub determineCrc32()
{
    my $buffer = $_[0];
    my $crc = $_[1];
    my $i = 0;
    my $val = 0;
    my $k = 0;
    
    for( $i = 0; $i < int(length($buffer) / 4); $i = $i + 1 )
    {
        $val =
            sprintf("%02X", ord(substr($buffer, ($i*4) + 0, 1))) .
            sprintf("%02X", ord(substr($buffer, ($i*4) + 1, 1))) .
            sprintf("%02X", ord(substr($buffer, ($i*4) + 2, 1))) .
            sprintf("%02X", ord(substr($buffer, ($i*4) + 3, 1)));
        
        $crc->badd(hex($val));
        $crc->bmod('0x100000000');
    }

    $val = "";
    $k = 0;
    for( 1 .. int(length($buffer) % 4) )
    {    
        $val .= sprintf("%02X", ord(substr($buffer, ($i*4) + $k, 1)));
        $k++;
    }

    # pad other bytes of 32bit with "00"
    for( 1 .. (4 - int(length($buffer) % 4)) )
    {
        $val .= "00";
    }

    $crc->badd(hex($val));
    $crc->bmod('0x100000000');
}
[download]

Would be very interesting for me how a good perl programmer would code this specific CRC. Because I don't think that my solution is a good way to solve it.

Greetings

Dirk

Comment on Re^4: CRC of a string Download Code

Replies are listed 'Best First'.
Re^5: CRC of a string by ikegami (Patriarch) on Nov 18, 2009 at 16:48 UTC
My god no! Just replace `% 0x100000000` [download] with `% (2**32)` [download]	[reply] [d/l] [select]
Re^5: CRC of a string by keszler (Priest) on Nov 18, 2009 at 17:09 UTC
`use strict; # solution: 990644297 my $buffer = "/etc/test2.sh"; my $crc = 0; for (grep $_, split /(.{1,4})/, $buffer) { my $val = sprintf "%02X"x4, map { ord } split //, $_; $crc += hex($val); $crc %= 2**32; } print $crc,$/;` [download]	[reply] [d/l]
Re^6: CRC of a string by ikegami (Patriarch) on Nov 18, 2009 at 18:54 UTC
`/(.{1,4})/` should be `/(.{1,4})/s` `grep $_, split /(.{1,4})/s, $buffer` is buggy. Fix: `$buffer =~ /(.{1,4})/sg` So much simpler too! `hex sprintf "%02X"x4, map { ord } split //, $_` can be simplified to `unpack 'N', "$_\0\0\0"` The latter should be much faster too.	[reply] [d/l] [select]