pop.mac

; **********************************************************************
; *                                                                    *
; * $POP(DUMMY) - POP INTEGER FROM STACK                               *
; *                                                                    *
; * $POP IS USEFUL IF A LEVEL OF STACK NEEDS TO BE REMOVED.            *
; * CONSIDER:                                                          *
; *                                                                    *
; *   ASSIGN 1 TO I        -- STORE ADDRESS OF LABEL 1 TO I            *
; *   CALL F(I)            -- PASS I TO SUBROUTINE F                   *
; * 1 ...                                                              *
; *                                                                    *
; *   SUBROUTINE F(I)                                                  *
; *   EXTERNAL $POP                                                    *
; *   INTEGER $POP                                                     *
; *   JUNK = $POP(0)       -- REMOVE RETURN ADDRESS                    *
; *   GO TO I              -- GO TO ASSIGNED LABEL I                   *
; *   END                                                              * 
; *                                                                    *
; * THIS CAN BE USED AS A REPLACEMENT FOR MULTIPLE RETURNS IN          *
; * FORTRAN IV THAT ARE MISSING IN FORTRAN-80                          *
; *                                                                    *
; * $DADSP AND $SPHL CAN BE USED TO IMPLEMENT CO-ROUTINES OR           *
; * CO-OPERATIVE MULTI-TASKING. THESE CAN ALSO BE USED TO ALLOCATE     *
; * STACK STORAGE, WHEN USED WITH $POP.                                *
; *                                                                    *
; * AGAIN, CONSIDER:                                                   *
; *                                                                    *
; *   IRET = $POP(0)       -- POP RETURN ADDRESS                       *
; *   IOLDSP = $DADSP(0)   -- SAVE OLD STACK POINTER                   *
; *   $SPHL($DADSP(-128))  -- ALLOCATE 128 BYTES ON STACK              *
; *   ISTOR = $DADSP(0)    -- BASE OF STACK STORAGE                    *
; *   CALL $PUSH(IRET)     -- PUT BACK RETURN ADDRESS                  *
; *                                                                    *
; * NOTE THAT ISTOR IS A POINTER LIKE VARPTR RETURNS. THIS CAN BE USED *
; * WITH PEEK/POKE AND AS A PARAMETER. SINCE THE STACK GROWS DOWN, THE *
; * ISTOR IS THE BASE OF THE STORAGE ON THE STACK.                     *
; *                                                                    *
; **********************************************************************
;
         .8080
         CSEG
;
         PUBLIC   $POP
;
; $POP(DUMMY) - RETURN TOP OF STACK AND REMOVE
;
; CONSIDER CALL $SPHL($DADSP(2)) WHICH IS EQUIVALENT BUT
; DOES NOT RETURN TOP OF STACK VALUE.
;
$POP:    POP      D		 ; RETURN ADDRESS
         POP      H              ; TOP OF STACK VALUE
         PUSH     D
         RET
;
         END