Rotate Field Dispatching Jump Table

This idiomatic macro usage generates a jump table with eight entries, one each for the eight possible codes in the rotate field of the operate instruction.

GP1.6    NULL
          ECHO   1,OPR=(INT1,BSW,RAL,RTL,RAR,RTR,ERR,ERR)
+         EQ     OPR

EQ is the CDC-6000's unconditinal jump instruction. The plus sign (+) insures that the jump is the first instruction of a new word, a placement called forced upper.

PDP-8 Simulator