BEGIN {
    my %n= ( 0..9, 'a'..'f', 1..9, 'a'..'f', 10 );

    sub incHex {
        s{
            ( [0-9a-fA-F] ) # Any hex digit followed by
            ( [fF]* )\b     # (always) trailing (optional) 'f's
        }{
            $n{ lc $1 } . '0' x length($2);
        }gex
            for  @_;
    }
}