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Re: Confusion about code sample in perlfaq4

by thundergnat (Deacon)
on Feb 22, 2013 at 19:36 UTC ( #1020211=note: print w/replies, xml ) Need Help??

in reply to Confusion about code sample in perlfaq4

The wording does seem to imply that it would return a list of bit values, but that isn't what it is doing. Rather, that routine returns a list of bit positions that are set (have a 1 in them).

If you just want the list of bits, it is probably simplest to split an unpacked string.

my @bits = split //, unpack "b*", $vec;

To furthur demonstrate:

use integer; my $vec = 42; my @ints; my $bits = unpack "b*", $vec; my @bits = split //, unpack "b*", $vec; push @ints, 0 if $bits =~ s/^(\d)// && $1; push @ints, pos $bits while($bits =~ /1/g); print "\n"; print join ', ', @ints; print " <-- bit positions set\n"; print join ', ', @bits; print " <-- bits \n";
2, 4, 5, 9, 12, 13 <-- bit positions set
0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0 <-- bits 

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