# PICMicrocontollerMathMethod

## Reciprocal 32768/x

from 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
cblock
x, yh, yl
endc

clrf x
;       movlw 129
;       movwf x
again
call Reciprocal8
nop
incf x, f
goto 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
movf x, w
skpnz
retlw 1        ;error - division by zero
movwf yh
clrf yl
setc
Reciprocal8a
rrf yl, f
rlf yh, f
skpc
goto Reciprocal8a

clrc
rrf yh, w
clrf yh
subwf yh, f
Reciprocal8b
rrf yh, f
rrf yl, f
skpc
goto Reciprocal8b
retlw 0         ;ok
;****************************************************

```

 file: /Techref/microchip/math/div/recip32k-ng.htm, 1KB, , updated: 2000/8/8 18:21, local time: 2019/9/16 16:12, TOP NEW HELP FIND:  100.26.182.28:LOG IN

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