;
; variable right shift

  INCLUDE "p18f242.inc"


;unsigned char vlshift(v,amt)
;unsigned char v, amt;
;{
;  while (amt) {
;   v = v << 1;
;   amt--;
;  }
;  return(v);
;}

;  Parameter space for main
 CBLOCK 0x020	
  i,j,k
 ENDC
  org    0

  ;; initialize software stack 
  ;; use FSR0 as software stack
  lfsr FSR0, 0x7f

  ; initialize main program variables
  movlw  0x24
  movwf  i     ; i = 0x24
  movlw  0x2
  movwf  j     ; j = 2
  
  ;; setup subroutine parms

  movf   j,w
  movwf  POSTDEC0  ; push amt value onto stack
  movf   i,w
  movwf  POSTDEC0  ;push v value onto stack
  call   vshift    
  movwf  k   ; k = vshift(v,amt);
  movf   PREINC0,f  ; pop amt off stack to clean up

here
  goto here

;; subroutines


;; return value in w
;; 'amt' at INDF0+2
;; 'v' at INDF0+1
vshift
  movlw  2         ;will use w to index to v
  movf   PLUSW0,f   ;test 'amt'
vshift_loop
  btfsc  STATUS,Z  ; amt==0?
  goto   vl_return
  bcf    STATUS,C
  movlw  1
  rlcf   PLUSW0     ; v = v << 1
  movlw  2
  decf   PLUSW0,f     ; amt--
  goto   vshift_loop
vl_return
  ;; 'v' has result, pop off into w reg
  ;; before return
  movf  PREINC0,w  ; w <- v
  return


  end

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