;
; ***************************************************************************
; ***  Bubble Software Parallax to PIC Source Converter. Copyright 1999.  ***
; ***  http://www.picnpoke.com                 email: sales@picnpoke.com  ***
; ***************************************************************************
;
             <<<<<<< ParaPIC ERROR Found >>>>>>>>
              device SX28,STACKX, OPTIONX, CARRYX  

;Fractional multiply. 
;This is a routine that multiplies two values, 
;  one treated as an integer, 
;  and the other treated as a binary fraction.

;Adapted from 6800 code by Ira Chayut. 
;BYTE Magazine, September 1976, Programming Quickies, page 124.

 org $10
arg1 Res 1
arg2 Res 1

 RESET Start
Start
             CLRF fsr                   
;test code: 255 * 2/3 ~= 170. Actually returns 166.
             MOVLW d'255'               
             MOVWF arg1
             MOVLW 256*2/3              
             MOVWF arg2
             CALL fracmul2              
;test code: 80 * 1/2 ~= 40. Actually returns 40.
             MOVLW d'80'                
             MOVWF arg1
             MOVLW 256*1/2              
             MOVWF arg2
             CALL fracmul2              
             GOTO $                     

fracmul
;This version depends on CARRYX being off.
             CLRW                       ;W=0
fracmul_mloop
             BCF status,c               
             RRF arg1                   ;ARG1:=ARG1/2
             BCF status,c               ; don't copy the carry
             RLF arg2                   ;CY:=MSB(ARG2), ARG2:=ASL(ARG2,1)
             BTFSC status,c             ;IF CY=0 THEN SKIP THE ADDITION
             ADDWF arg1,w               ;ELSE W:=W+ARG1
; CARRYX must be off.
             MOVF arg2                  
             BTFSS status,z             ;IF ARG2 NE 0 THEN REITERATE
             GOTO @_mloop
             RETLW 0h                   ;ELSE RETURN WITH RESULT IN W

fracmul2
;Version not sensitve to CARRRYX
             CLRW                       ;W=0
fracmul2_loop
             BCF status,c               
             RRF arg1                   ;arg1 = arg1 / 2
             BCF status,c               
             BTFSC arg2,d'7'            ;if arg2 <= 128
             ADDWF arg1,w               ; W = W + arg1
             BCF status,c               
             RLF arg2                   ;arg2 = arg2 * 2
             MOVF arg2                  ;if arg2 <> 0
             BTFSS status,z             ; goto loop
             GOTO @_loop
             RETLW 0h                   ;return


             
             
             end