switch (len) {
case 32:
b = ((b & 0xffff0000) >> 16) | ((b & 0x0000ffff) << 16);
+ /* fall through */
case 16:
b = ((b & 0xff00ff00) >> 8) | ((b & 0x00ff00ff) << 8);
+ /* fall through */
case 8:
b = ((b & 0xf0f0f0f0) >> 4) | ((b & 0x0f0f0f0f) << 4);
+ /* fall through */
case 4:
b = ((b & 0xcccccccc) >> 2) | ((b & 0x33333333) << 2);
+ /* fall through */
case 2:
b = ((b & 0xaaaaaaaa) >> 1) | ((b & 0x55555555) << 1);
case 1: