# PICMicrocontollerMathMethod

From: Scott Dattalo

``` ;******************************************
;
; Computes  z = x + y
; where x,y,z are all 8-bit packed BCD numbers
; Exits with C=1 if x+y > 0x99 and with z=1 if
; x+y = 0x100.
; Note that z can be aliased to x or y so that
;it's possible to calculate x = x+y or y = x+y
;This routine forms the BCD two's complement of
;y and then uses the bcd_subtract routine to
;find the sum. e.g. z = x - (-y) = x + y
;
; 10 cycles
COMF    y, W    ;W = ~y
ADDLW   0x9a+1  ;W = ~y + 0x9a +1
;W = (~y + 1) + 0x9a
;W = 0x9a - y
SUBWF   x, W    ;W = x - (0x9a - y)
;W = x + y - 0x9a
;W = x + y + 0x66
RLF     z, F    ;Get the carry
SKPDC           ;if lsn of x + lsn of y < 10 (dec)
BTFSS   z, 0    ;Similarly for the msn
RRF     z, F    ;restore the carry
MOVWF   z

RETURN

```

 file: /Techref/microchip/math/add/bcdp2.htm, 1KB, , updated: 2000/2/11 14:56, local time: 2024/2/28 05:11, TOP NEW HELP FIND:  3.237.34.21:LOG IN

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