@a=(1,2,3,0); $x=0; $m=4;
timethese(-10,{ ixwheel=> q{ $x = $a[$x] }
               modby2x1=> q{ $x = (++$x) & $m} });
 ixwheel: 434505.60/s
modby2x1: 391856.16/s

timethese(-10,{ ixwheel=> q{ $x=$a[$x] }
               modby2x2=> q{ $x++; $x &= $m }});
 ixwheel: 433011.28/s
modby2x2: 539474.07/s