# SXMicrocontrollerMathMethod

## BCD (packed) addition

From: Scott Dattalo

Translated and optimized for the Scenix SX by Nikolai Golovchenko

```;******************************************
;bcd_add
;
; Computes  x = x + y
; where x and y are all 8-bit packed BCD numbers
; Exits with C=1 if x+y > 0x99 and with z=1 if
; x+y = 0x100 or x+y = 0.
;
; Size: 15 instructions
; Execution time including return: 14/15 cycles

bcd_add
mov	W, #\$66	;x = x + y + 0x66
add	W, y
add	x, W

clr	W
sb	DC		;if lsn of x + lsn of y < 10 (dec)
or	W, #\$06	;then remove the extra 6 added above
snb	C		;Similarly for the msn
jmp	bcd_add2

or	W, #\$60
sub	x, W		;correct result
clrb	C		;restore carry
ret
bcd_add2
sub	x, W		;correct result
setb	C		;restore carry
ret
```

If you don't need to check the carry the routine can be simplified:

```;******************************************
;bcd_add_nc
;
; where x and y are all 8-bit packed BCD numbers
; Exits with z=1 if x+y = 0x100 or x+y = 0.
;
; Size: 10 instructions
; Execution time including return: 12 cycles

bcd_add_nc
mov	W, #\$66	;x = x + y + 0x66
add	W, y
add	x, W

clr	W
sb	DC		;if lsn of x + lsn of y < 10 (dec)
or	W, #\$06	;then remove the extra 6 added above
sb	C		;Similarly for the msn
or	W, #\$60

sub	x, W		;correct result
ret
```

If you don't want to influence input registers, the following routine computes s = x + y:

```;******************************************
;bcd_add_to
;
; Computes  s = x + y
; where x and y are all 8-bit packed BCD numbers
; Exits with C=1 if x+y > 0x99 and with z=1 if
; x+y = 0x100 or x+y = 0.
;
; Size: 16 instructions
; Execution time including return: 15/16 cycles

bcd_add_to
mov	W, #\$66	;x = x + y + 0x66
add	W, y
add	W, x
mov	s, W

clr	W
sb	DC		;if lsn of x + lsn of y < 10 (dec)
or	W, #\$06	;then remove the extra 6 added above
snb	C		;Similarly for the msn
jmp	bcd_add_to2

or	W, #\$60
sub	s, W            ;correct result
clrb	C		;restore carry
ret
bcd_add_to2
sub	s, W		;correct result
setb	C		;restore carry
ret

```

Comments:

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