Homework 6 Solutions

22C:18, Summer 1997

1. I/O was not discussed, nor was addressing of any but simple variables. That is, there was no discussion of array addressing, pointers, or other data structures! Character and other non-integer operations were also omitted.

2. Using the following (bad) idea:
   • Set aside R1-2 as short-term temporaries
   • Set asider R3 as the frame pointer
   • Set aside R4 as the stack pointer
   The following macros suffice:

   MACRO add
     ADDSI R4,-4
     LOADS R1,R4
     LOAD  R2,R4,-4
     ADD R2,R1,R2
     STORE R2,R4,-4
   ENDMAC
   
   MACRO sub
     ADDSI R4,-4
     LOADS R1,R4
     LOAD  R2,R4,-4
     SUB R2,R2,R1
     STORE R2,R4,-4
   ENDMAC
   
   MACRO pushimm =c
     LIL    R1,c
     STORES R1,R4
     ADDSI  R4,-4
   ENDMAC
   
   MACRO pushlocal var
     LOAD	R1,R3,var
     STORES R1,R4
     ADDSI  R4,-4
   ENDMAC
   
   MACRO bne lab
     ADDSI  R4,-4
     LOADSCC R1,R4
     BNE lab
   ENDMAC
   
   MACRO function name
     name:
   ENDMAC
   
   MACRO funcreturn
     ADDSI  R4,-4
     LOADS  R1,R4	; temp = pop()
     MOVE   R4,R3  ; SP = FP
     ADDSI  R4,-4
     LOADS  R3,R4  ; FP = pop()
     ADDSI  R4,-4
     LOADS  R2,R4	; temp1 = pop()
     STORES R1,R4  ; push(temp)
     ADDSI  R4,4
     JUMPS  R2	; PC = temp1
   ENDMAC
   
   MACRO pushmark
     STORES R0,R4
     ADDSI  R4,4	; push(0)
     STORES R3,R4
     ADDSI  R4,4   ; push(FP)
   ENDMAC
   
   MACRO paramcall func,params
     LIS	 R1,params << 2
     SUB    R3,R4,R1  ; FP = SP - (params << 4)
     LEA    R1,.+8    ; M[FP - (2 << 4)] = returnPC
     JUMP   func      ; PC = func
   		   ; .+8 sets return point to here!
   ENDMAC
   

3. Here is a more efficient version of pushlocal that uses the proper load immediate instruction depending on the value of its parameter.

   MACRO pushlocal =c
     IF    (c < -128) ! (c > 128)
       IF  (c < -#800000) ! (c > #FFFFFF)
         LIL    R1,const
       ELSE
         LIW    R1,const
       ENDIF
     ELSE
       LIS    R1,const
     ENDIF
     STORES R1,R4
     ADDSI  R4,-4
   ENDMAC
   

4. Here is a main program to call the procedure written using the above macros.

   START:	LOAD	R2,PSTACK
   	CALL	DSPINI
   
   	; change gears to funny calling sequence
   	MOVE	R4,R2	; switch stack pointer to new register
   	LEA	R1,RA	; push return address
   	STORES	R1,R4
   	ADDSI	R4,4
   	ADDSI	R4,4	; push nothing (we have no frame that matters)
   	MOVE    R3,R4   ; set up frame pointer for function
   	LIS	R1,3	; push a parameter
   	STORES	R1,R4
   	ADDSI	R4,4
   	LIS	R1,4	; push another parameter
   	STORES	R1,R4
   	ADDSI	R4,4
   	JUMP	multiply
   RA:
   	ADDSI	R2,-4
   	LOADS	R3,R2	; pop result into R3
   
   	; change gears back from funny calling sequence
   	MOVE	R2,R4	; switch stack pointer back home
   
   	; output result gears back from funny calling sequence
   	LIS	R4,5
   	CALL	DSPDEC
   
   	; now, do it again, different numbers
   
           ; change gears to funny calling sequence
           MOVE    R4,R2   ; switch stack pointer to new register
           LEA     R1,RA1  ; push return address
           STORES  R1,R4
           ADDSI   R4,4
           ADDSI   R4,4    ; push nothing (we have no frame that matters)
           MOVE    R3,R4   ; set up frame pointer for function
           LIS     R1,4    ; push a parameter      
           STORES  R1,R4
           ADDSI   R4,4
           LIS     R1,5    ; push another parameter
           STORES  R1,R4
           ADDSI   R4,4
           JUMP    multiply
   RA1:
           ADDSI   R2,-4
           LOADS   R3,R2   ; pop result into R3
   
           ; change gears back from funny calling sequence
           MOVE    R2,R4   ; switch stack pointer back home
   
           ; output result gears back from funny calling sequence
           LIS     R4,5
           CALL    DSPDEC
   
   	; quit
   	LIS	R1,0
   	JUMPS	R1