I can't (yet) work out how to code _next() in Perl.

#! perl -slw
use strict; 
use Inline C => Config => BUILD_NOISY => 1;
use Inline C => <<'END_C',  NAME => '_1059792', CLEAN_AFTER_BUILD =>0;

unsigned int _next( unsigned int v ) {
    unsigned int t = (v | (v - 1)) + 1;
    unsigned int w = t | ((((t & -t) / (v & -v)) >> 1) - 1);
    return w;
}

END_C

sub permIt {
    my $l = @_;
    my @chars = grep $_ ne '-', @_;
    my $n = my $s = ( 1 << @chars ) -1;
    do {
        my $bits = pack 'V', $n;
        my @copy = @chars;
        my $str = join '', map{
            vec( $bits, $_, 1 ) ? shift( @copy ) : '-'
        } 0 .. $l-1;
        print $str;
        $n = _next( $n );
    } until( $n > ( $s << ( $l - @chars ) ) );
}

permIt( split '', 'ABC---' );;

__END__
ABC---
AB-C--
A-BC--
-ABC--
AB--C-
A-B-C-
-AB-C-
A--BC-
-A-BC-
--ABC-
AB---C
A-B--C
-AB--C
A--B-C
-A-B-C
--AB-C
A---BC
-A--BC
--A-BC
---ABC
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