## Divider in App Note 200

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Looking at the divider in App Note 200, I think it's putting the result in dd16ul and dd16uh instead of dres16ul and dres16uh, or am I daft? :roll: I don't even see it touching the dres.. registers.

Torby

;***************************************************************************
;*
;* "div16u" - 16/16 Bit Unsigned Division
;*
;* This subroutine divides the two 16-bit numbers
;* "dd8uH:dd8uL" (dividend) and "dv16uH:dv16uL" (divisor).
;* The result is placed in "dres16uH:dres16uL" and the remainder in
;* "drem16uH:drem16uL".
;*
;* Number of words :19
;* Number of cycles :235/251 (Min/Max)
;* Low registers used :2 (drem16uL,drem16uH)
;* High registers used :5 (dres16uL/dd16uL,dres16uH/dd16uH,dv16uL,dv16uH,
;* dcnt16u)
;*
;***************************************************************************

;***** Subroutine Register Variables

.def drem16uL=r14
.def drem16uH=r15
.def dres16uL=r16
.def dres16uH=r17
.def dd16uL =r16
.def dd16uH =r17
.def dv16uL =r18
.def dv16uH =r19
.def dcnt16u =r20

;***** Code

div16u: clr drem16uL ;clear remainder Low byte
sub drem16uH,drem16uH;clear remainder High byte and carry
ldi dcnt16u,17 ;init loop counter
d16u_1: rol dd16uL ;shift left dividend
rol dd16uH
dec dcnt16u ;decrement counter
brne d16u_2 ;if done
ret ; return
d16u_2: rol drem16uL ;shift dividend into remainder
rol drem16uH
sub drem16uL,dv16uL ;remainder = remainder - divisor
sbc drem16uH,dv16uH ;
brcc d16u_3 ;if result negative
clc ; clear carry to be shifted into result
rjmp d16u_1 ;else
d16u_3: sec ; set carry to be shifted into result
rjmp d16u_1

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Quote:

.def dres16uL=r16
.def dres16uH=r17
.def dd16uL =r16
.def dd16uH =r17

1) Note that those are two names for the same registers. [It reduces the register usage, but could be split depending on your register usage conventions.]

2) Try to use the "Code" form when posting code fragments to preserve the formatting.

3) There was a bug in one of Atmel's app notes on arithmetic. I don't remember whether it was fixed or not, or exactly which app note. IIRC it should be a post lower than 5000 or so--the early days of the Forum.

Lee

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I've never met a pig I didn't like, as long as you have some salt and pepper.