csd_mul_int.s43

MSP430Appliction Note

;******************************************************************************
;   MSP430FG439 Integer-Integer multiplication using Horner's Algorithm using CSD format
;
;   Description: This code performs a 16-bit integer-integer multplication 
;                of numbers to return an 16-bit integer
;                 
;
;   Note:        This code assumes 32.768kHz XTAL on LFXT1 on the MSP430FG439 
;
;                 MSP430FG439
;               -----------------
;              |              XIN|-  
;              |                 | 32.768kHz
;              |             XOUT|-
;              |                 |
;
;
;   K. Venkat
;   Texas Instruments Inc.
;   July 2006
;   Built with IAR Embedded Workbench Version: 3.41A
;*******************************************************************************/
            public mul_csd_int
        
	    RSEG CODE
mul_csd_int:

            mov.w     R12,R13               ; The operand "input" in register R12 
            rla.w     R13
            rla.w     R13
            rla.w     R13
            sub.w     R12,R13               ; X1=X*2^3-X
            rla.w     R13
            rla.w     R13
            rla.w     R13
            sub.w     R12,R13               ; X2=X1*2^3-X
            rla.w     R13
            rla.w     R13
            rla.w     R13
            add.w     R12,R13               ; Final result=X3=X2*2^3+X
            mov.w     R13,R12               ; The final answer returned to the 
                                            ; calling function
        
            ret
            END