;                     BITTER.MAC
;
;  A SUBROUTINE TO DO OPERATIONS ON THE BIT LEVEL
;
;  USE BY SAYING:  CALL BITTER(NUMBER, OFFSET, OPERATION)
;  IF OPERATION = 1, WANT TO SET BIT OFFSET OF BITS 1 THROUGH 16
;  IF OPERATION = 2, WANT TO CLEAR IT
;  IF OPERATION = 3, ARE TESTING IT TO SEE IF BIT IS SET
;  FOR THIS OPERAATION, USE IT BY SAYING, J=BITTER(NUMBER,OFFSET,3)
;       J WILL BE 1 IF THE DESIRED OFFSET IS SET
;       J WILL BE 0 IF THE DESIRED OFFSET IS NOT SET
;       WHEN USING IT IN THIS WAY, BE SURE TO DEFINE BITTER AS AN INTEGER
;
        .GLOBL  BITTER
        .TITLE  BITTER
BITTER: MOV     @2(R5),R1                ; MOVE THE NUMBER TO R1
        MOV     #1,R2                    ; THIS WILL BE THE NO TO SET OR CLEAR
        MOV     @4(R5),R3                ; MOVE OFFSET TO R3
        DEC     R3
        ASH     R3,R2                    ; R2 NOW CONTAINS THE WORD TO SET
        CMP     @6(R5),#1                ; DO WE WANT TO SET THE BIT
        BEQ     SET
        CMP     @6(R5),#2                ; DO WE WANT TO CLEAR THE BIT
        BEQ     CLEAR
        CMP     @6(R5),#3                ; DO WE WANT TO TEST TO SEE IF SET
        BEQ     TEST
        RETURN
SET:    BIS     R2,R1
        MOV     R1,@2(R5)
        RETURN
CLEAR:  BIC     R2,R1
        MOV     R1,@2(R5)
        RETURN
TEST:   BIT     R2,R1
        BNE     OFF
        CLR     R0
        RETURN
OFF:    MOV     #1,R0
        RETURN
        .END