On Nov 11, 11:27 pm, c...@pobox.com (Chap Harrison) wrote:
> I'm almost embarrassed to ask this, but I can't figure out a simple way to
> construct a switch ('given') statement where the 'when' clauses involve
> bit-testing.
>
> Here's the only way I've figured out to build a switch statement that does
> the trick. It seems unusually wordy, which makes me think there must be a
> simpler way to test for certain bit combinations. Any suggestions?
>
> Thanks,
> Chap
>
> #!/usr/bin/perl
>
>
>
> use strict;
> use warnings;
> use feature ":5.10";
>
> # Here are masks for various bit combos of interest:
>
>
>
> my $one_three = 0b00001010; # bits 1 and 3 (counting from 0, right to
> left)
>
> my $zero_four = 0b00010001; # bits 0 and 4
>
>
> my $five = 0b00100000; # bit 5
>
>
>
> # Here we will test several bit fields for bit combos of interest:
>
>
>
> for my $flags ( 0b10111010, 0b10111000, 0b10010010) {
>
> my $asbits = sprintf("0b%08b", $flags); # prepare bits for
> pretty-printing
>
>
> given ( $flags ) {
> when ( ($_ & $one_three) == $one_three ) { # bits one and three are
> on
>
> say "$asbits has bits 1 and 3";
> }
> when ( ($_ & $zero_four) == $zero_four ) { # bits zero and four are
> on
>
> say "$asbits has bits 0 and 4";
> }
> when ( ($_ & $five) == $five ) { # bit five is on
>
>
> say "$asbits has bit 5";
> }
> default {
> say "$asbits has no interesting bit patterns.";
> }
> }
>
> }
Not lots shorter but you could use a closure to hide
the calculation:
my $mask;
for my $flags ( ... ) {
$mask = sub { return ($flags & $_[0]) == $_[0] }
unless $mask;
given( $flags ) {
when ( $mask->($one_and_three) ) { ... }
when ( $mask->($zero_and_four) ) { ... }
...
}
}
--
Charles DeRykus
