# SXMicrocontrollerBasic Division MathMethods

## by Nikolai Golovchenko

Don't know how to explain its operation, but what it does is approximate calculation of 32768/x using linear interpolation between points where x=1,2,4,8,16,32,64,128,256.

The routine can be extended for other number of bits in x.

```;test
ORG
x               DS	1
yh              DS	1
yl              DS	1

clr	x
;	mov	W, #129
;	mov	x, W
again
call	reciprocal8
nop
inc	x
jmp	again

;****************************************************
;
; Approximate calculation of 32768/x
; Input: x
; Output: y = 256 * yh + yl ~= 32768/x
;
; To calculate reciprocal, linear interpolation
; is used between points, where x=1,2,4,8,16,32,64,128
;
; Size: 19 instructions
; Execution speed(worst case including return):
;  6+4*8-1+4+4+2=47
;
; 4 Aug 2000 by Nikolai Golovchenko
;****************************************************
reciprocal8
mov	W, x
snz
retw	1	;error - division by zero
mov	yh, W
clr	yl
stc
reciprocal8a
rr	yl
rl	yh
sc
jmp	reciprocal8a

clc
mov	W, >>yh
clr	yh
sub	yh, W
reciprocal8b
rr	yh
rr	yl
sc
jmp	reciprocal8b
retw	0	;ok
;****************************************************

```

 file: /Techref/scenix/lib/math/reciprocal.htm, 1KB, , updated: 2004/11/4 15:31, local time: 2024/7/24 11:43, TOP NEW HELP FIND:  44.192.44.30:LOG IN

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