in reply to Re^3: ECC computation
in thread ECC computation

If you want speed this up, you might wanna try unpack's template for counting bits.

perlpacktut#Doing-Sums

And an even parity bit can be determined like this:

my $evenparity = unpack( '%1b*', $mask );

And you could use & to isolate the right bits with pre-calculated bit-masks.

PS: not sure why you use B64 for 32bit hex.

update

that's a weak demo because I don't seem to get MSB and LSB right.

  DB<85> $n=pack 'h8', '3E10F67A'

  DB<86> undef $m0; vec($m0,$_,1)=1 for  0, 1, 3, 4, 6, 8, 10, 11, 13,
+ 15, 17, 19, 21, 23, 25, 26, 28, 30

  DB<87> say unpack 'b32',$_ for $n, $m0, $n & $m0
11000111100000001111011011100101
11011010101101010101010101101010
11000010100000000101010001100000

  DB<88> p unpack '%1b', $n & $m0
1

[download]

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

Replies are listed 'Best First'.
Re^5: ECC computation
by choroba (Cardinal) on Jan 05, 2020 at 21:35 UTC
    Yes, I'm not a frequent user of pack and unpack so I often forget what tricks they can do. So, here's the full solution, more than five times faster than my previous one: 
    my @masks = qw( 11011010101101010101010101101010
                10110110011011001100110011011001
                01110001111000111100001111000111
                00001111111000000011111111000000
                00000000000111111111111111000000
                00000000000000000000000000111111
                11111111111111111111111111111111 );
sub ecc {
    my ($hex) = @_;
    my $d = unpack 'B32', pack 'H8', $hex;
    my @r;
    push @r, unpack '%1B*', $_ & $d for @masks;
    $r[-1] = unpack '%1B*', $r[-1] . join "", @r[ 0 .. $#r - 1 ];
    return join "", @r
}

    [download]
    map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
[reply]
[d/l]
[select]
      > more than five times faster than my previous one:

      Cool, it works?

      > Yes, I'm not a frequent user of pack and unpack

      neither am I, so I left it to you ... ;-)

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

[reply]
        > Cool, it works?

        It works the same way as my previous solutions. The specification was vague and there were no test cases, so I'm waiting for the OP to confirm its correctness.

        Update: BTW, have you noticed the id of your node (as well as this one) is a possible output?

        map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
[reply]
[d/l]

In Section Seekers of Perl Wisdom