intel hex record 1

[bc819]

Does anyone know how to write a perl script to do a checksum calculation of an intel hex record?
The intel hex record format is:
:BBAAAATTDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDCC
where
BB = 2 digit byte count
AAAA = 4 digit hex address
TT = 2 digit hex record type
DD = 2 digit hex data byte
CC = 2 digit checksum byte
The checksum is calculated by summing the values of all hexadecimal digit pairs in the record and taking the two's complement.
for example:
intel record:
:1000F000FF3FFF3FFF3FFF3FFF3FFF3FFF3FFF3F10
sum of all hex bytes except the checksum:
10+00+F0+00+FF+3F+...+FF+3F = AF0
2's compliment of F0 is 10

Thanks.

 

[KevinADC]

I'm a little out of my depth here, but maybe this is what you want:

http://search.cpan.org/~simkin/Apache-LoggedAuthDBI-0.12/MD5.pm

 

[bc819]

Thanks, KevinADC.
However, the script i'm looking for is not that complicated. All I need is to convert 2 char in the string to hex and then add them all up, then negate the number and add 1 to it. Take the LSB and put it back to the end of the string. That is it.
I'm reading the Perl Cookbook right now. Hope i'll come up with somethng soon.

 

[rharsh]

I'm sure there's a great way to use unpack to deal with your string of hex characters, but I don't know how; so it's a regex instead. This code will calculate the sum of that string.

my $str = '1000F000FF3FFF3FFF3FFF3FFF3FFF3FFF3FFF3F10';
my $check = substr($str,length($str)-2,2, ""); #Strip Checksum
my $sum;
$sum += hex($_) for $str =~ /(.{2})/gc;
printf '%i - %x', ($sum) x 2

I'm still working on the 2's complement bit.

 

[rharsh]

This is kind of ugly looking, but it appears to work.

my $str = '1000F000FF3FFF3FFF3FFF3FFF3FFF3FFF3FFF3F10';
my $check = substr($str,length($str)-2,2, ""); #Strip Checksum
my $sum;
$sum += $_ for unpack('C*', pack("H*", $str));
my $hex_sum = sprintf "%x", $sum;
print "$sum - $hex_sum\n";
print "Check: $check - ", two_comp(), "\n";

# Calculates 2's complement for last 2 characters of hex string
sub two_comp {
    my $hex = substr $_[0], length($_[0]) - 2, 2;
    my $bin = unpack('B*', pack("H*", $hex));
    $bin =~ s/(.)/($1 xor 1) || 0/ge;
    my $dec = unpack('C*', pack("B*", $bin));
    $dec++;
    return unpack('H*', pack('C*', $dec));
}

 

[KevinADC]

I don't know what the heck I wa thinking but rharsh bailed me out, thanks mate. A star is in order.

 

[rharsh]

I know the feeling Kevin, when I read this post at first I said to myself "it supposed to do what?!" There probably is a module to do something similar, but reinventing the wheel every once in a while can be fun.

I do have a question for you, bc819 - what is the 2's complement function supposed to return if you pass in '00'? Following the algorithm you gave above:

Invert the bits: 0000 0000 becomes 1111 1111 (FF)

Add one: Well, you end up with 0000 0001 0000 0000 (100)

Since the definition of your hex record is that there's only one hex value to use as a checksum - so, again, what is &two_comp('00') supposed to return?

 

[bc819]

&two_comp('00') should return (00). rharsh, thanks for the srcipt.

 

[bc819]

rharsh, please take a look at my mod on your code, I used the xor to compute 2's complement.
Thanks again for your effort.


my $str = '1000F000FF3FFF3FFF3FFF3FFF3FFF3FFF3FFF3F10';
my $check = substr($str,length($str)-2,2, ""); #Strip Checksum
my $sum;
$sum += $_ for unpack('C*', pack("H*", $str));
my $hex_sum = sprintf "%x", $sum;
print "$sum - $hex_sum\n";
$hex_sum = substr($hex_sum, -2); # just save the last byte of sum
$chksum = (hex($hex_sum) ^ 0xFF) + 1; # 2's complement of hex_sum
print "chksum is $chksum\n";
$chksum = sprintf("%2x",$chksum); # convert checksum to string
my $str = $str.$chksum; # put is back to the end of string, done
print"$str\n";

 

[bc819]

help...
$chksum = sprintf("%2x",$chksum); works fine when chksum is greater than 0x0f. If it's less than 0x10, the leading 0 does not show up in the string, only a space and the digit is appended at the end of the string. Any idea how to correct this problem?
Thanks

 

[bc819]

problem fixed:
added a line:
$chksum =~ s/ /0/g;
before append it to $str