horner_mul_float.s43

MSP430Appliction Note

;******************************************************************************
;   MSP430FG439 Integer-Float multiplication using Horner's Algorithm 
;
;   Description: This code performs a 16-bit integer-float 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_horner_float

	    RSEG CODE
mul_horner_float

            ; Integer part
        
            mov.w     R12,R13               ; The operand "input" in register R12 
            rla.w     R13             
            add.w     R12,R13               ; X1=X*2^1+X
            rla.w     R13
            rla.w     R13
            add.w     R12,R13               ; X2=X1*2^2+X
            rla.w     R13
            add.w     R12,R13               ; X3=X2*2^1+X
            rla.w     R13
            add.w     R12,R13               ; X4=X4*2^1+X
            rla.w     R13
            rla.w     R13
            rla.w     R13
            add.w     R12,R13               ; X5=X4*2^3+X, R13 has intermediate 
                                            ; result due to integer part 441
        
            ; Fractional Part
        
            mov.w     R12,R14               ; The operand "input" in register R12 
            rra.w     R14
            rra.w     R14
            rra.w     R14
            add.w     R12,R14               ; X1=X*2^-3+X  
            rra.w     R14
            add.w     R12,R14               ; X2=X1*2^-1+X
            rra.w     R14
            rra.w     R14
            add.w     R12,R14               ; X3=X2*2^-2+X
            rra.w     R14
            rra.w     R14
            add.w     R12,R14               ; X4=X3*2^-2+X
            rra.w     R14
            add.w     R12,R14               ; X4=X3*2^-1+X
            rra.w     R14                   ; X5=X4*2^-1
            add.w     R14,R13               ; Intermediate results added to give 
                                            ; final result
            mov.w     R13,R12               ; The final answer returned to the 
                                            ; calling function
        
            ret
            END