$signal = ($? & 0x7F00) >> 8;

00000000 00000000 CSSSSSSS EEEEEEEE

   & 0x00007F00

00000000 00000000 01111111 00000000 = 0x00007F00
00000000 00000000 0SSSSSSS 00000000

   >> 8

00000000 00000000 00000000 0SSSSSSS