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Reading Binary

by BoulderBuff64 (Novice)
on Jun 15, 2011 at 15:55 UTC ( #909797=perlquestion: print w/ replies, xml ) Need Help??
BoulderBuff64 has asked for the wisdom of the Perl Monks concerning the following question:

Oh Wise and Mighty Perl Monks,

Bit of a n00b here.

I have a binary input and would like to use that input to reference a block of information. A mock example: 1111 = ABCD. If given 0101 it would return B, D. If given 1001 it would return A, D.

I thought I could have the script go bit by bit: x1xx => print B. But I don't know the best way to do that.

Please advise,


Comment on Reading Binary
Re: Reading Binary
by toolic (Chancellor) on Jun 15, 2011 at 16:18 UTC
    One way to move through all characters in a string is with substr:
    use warnings; use strict; my $str = 'ABCD'; while (my $mask = <DATA>) { chomp $mask; for my $i (0 .. length($mask)-1) { print substr($str, $i, 1) if substr($mask, $i, 1) eq '1'; } print "\n"; } __DATA__ 1001 1110 0101 0001
      I think the OP is asking about binary data, not character data that contains '0' and '1'?
Re: Reading Binary
by oxone (Friar) on Jun 15, 2011 at 16:18 UTC
    Not a complete solution, but a hint to point you in the right direction:
    use strict; use warnings; my $byte = 'X'; my $binary = unpack('b*', $byte); print $binary; # prints 00011010
Re: Reading Binary
by duelafn (Priest) on Jun 15, 2011 at 16:30 UTC

    You can use vec for this

    #!/usr/bin/perl use strict; use warnings; my @letter = 'A'..'Z'; my $bits = pack "b*", "1001"; for (0..8*length($bits)-1) { print $letter[$_] if vec($bits,$_,1); } print "\n";

    Good Day,

      This is the method I ended up using. Thanks!
Re: Reading Binary
by TomDLux (Vicar) on Jun 15, 2011 at 16:38 UTC

    Given some input string representing a binary number, $bin, verify it only contains 1 & 0, to protect little Bobby Tables, then convert to an ordinary number. You only have 15 values to deal with, so you can hardcode an array. If it's 10 to 20 bits, you can precompute the array; if it's more, probably better to stick with calculating things as you need them, possibly with memoizing.

    my @block = qw( D C CD B BD BC BCD A AD AC ACD AB ABD ABC ABCD ); unshift @block, ''; # empty string for 0 $bin =~ m{([01]+)}; # untaint input my $idx = eval "0b$1"; my $result = $block[$idx];

    As Occam said: Entia non sunt multiplicanda praeter necessitatem.

      $bin =~ m{([01]+)}; # untaint input my $idx = eval "0b$1";

      1. You shouldn't use the results of a regular expression unless you verify that it matched correctly.
      2. Why use string eval when oct is less dangerous and provides the same result.

Re: Reading Binary
by AnomalousMonk (Monsignor) on Jun 15, 2011 at 20:35 UTC

    The comment in the  extract() function below says it works for a binary mask in the range 0 .. 255 (i.e., an 8-bit mask, and it does), but I think it will work with up to a 31-bit mask (but this is untested). The test suite is not complete; add your own examples.

Re: Reading Binary
by Marshall (Prior) on Jun 16, 2011 at 09:05 UTC
    Another way to shift through the ascii bit pattern is with split. A split on //, separates a string into individual characters.
    #!/usr/bin/perl -w use strict; my @ltrs = qw (A B C D); my $num = "0101"; print "$num=>"; my $i =0; foreach my $bit (split(//,$num)) { print $ltrs[$i] if $bit; $i++; } print "\n"; # prints: 0101=>BD
    I did not get the impression that the OP was interested in doing actual binary to decimal conversion although jwkrahn's suggestion of: $decimal = oct( "0b$input" ); looks like a "winner" to me in the case of ASCII strings.

    I would like to hear more about the application if these bits or combinations of bits represent something other than just a number. I probably would have some suggestions in that event, but want to hear more before running off on a tangent.

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