from Nikolai Golovchenko
;Division of 16bit by 8 bit with a result in Q16.16 form
;
; X_Int.X_Frac = X_Int / Y
;
; RAM - 6 bytes (1 temp):
; X_Int = X_IntH:X_IntL 16 bit input/ output integer part
; X_Frac = X_FracH:X_FracL 16 bit output fractional part
; Y divisor / temporary
; Counter counter
;
; Size = 39 instructions
; Execution time = 6+16*14-1+3+16*14-1+3+2(return)
; = 460 instruction cycles
;
; 8-July-2000 by Nikolai Golovchenko
; 16-February-2001 fixed, reduced execution time and temporaries
Div16by8to16_16
clrf X_FracL
clrf X_FracH
movlw 16
movwf Counter
movf Y, w ;keep Y value in accumulator
clrf Y ;and use Y register as temporary
;Find integer part
Div16by8to16_16a
rlf X_IntL, f ;shift next msb into temporary
rlf X_IntH, f
rlf Y, f
rlf Counter, f ;carry has 9th bit of temporary
;copy carry to counter
subwf Y, f ;substract Y (in w) from temporary
skpnc ;if no borrow, set Counter.0
bsf Counter, 0
btfss Counter, 0 ;if Counter.0 clear (borrow) restore temporary
addwf Y, f
clrc ;restore counter
rrf Counter, f
;at this point carry is the next bit of result
decfsz Counter, f ;repeat 16 times to find integer part
goto Div16by8to16_16a
;shift last integer bit
rlf X_IntL, f
rlf X_IntH, f
;Find fractional part
bsf Counter, 4 ;Counter = 16
Div16by8to16_16b
;Shift zero bit into temporary
rlf X_FracL, f
rlf X_FracH, f
rlf Y, f
rlf Counter, f ;carry has 9th bit of temporary
;copy carry to counter
subwf Y, f ;substract Y(in w) from temporary
skpnc ;if no borrow, set Counter.0
bsf Counter, 0
btfss Counter, 0 ;if Counter.0 clear (borrow) restore temporary
addwf Y, f
clrc ;restore counter
rrf Counter, f
decfsz Counter, f ;repeat 16 times
goto Div16by8to16_16b
;shift last fractional bit
rlf X_FracL, f
rlf X_FracH, f
movwf Y ;restore divisor
return
Questions:
This code did not work as expected. I send you the whole code.
list p=16F84A ; list directive to define processor
#include <p16F84a.inc> ; processor specific variable definitions
__CONFIG _CP_OFF & _WDT_OFF & _PWRTE_OFF & _XT_OSC
;***** VARIABLE DEFINITIONS
;w_temp EQU 0x0C ; variable used for context saving
;status_temp EQU 0x0D ; variable used for context saving
;**********************************************************************
cblock 0x0C
w_temp
status_temp
X_IntH
X_IntL
X_FracH
X_FracL
Counter
Y
endc
;**********************************************************************
RESET_VECTOR CODE 0x0000 ; processor reset vector
goto Start ; go to beginning of program
ISR CODE 0x0004 ; interrupt vector location
Interrupt:
movwf w_temp ; save off current W register contents
movf STATUS,w ; move status register into W register
movwf status_temp ; save off contents of STATUS register
; Place ISR Here
movf status_temp,w ; retrieve copy of STATUS register
movwf STATUS ; restore pre-isr STATUS register contents
swapf w_temp,f
swapf w_temp,w ; restore pre-isr W register contents
retfie ; return from interrupt
MAIN_PROGRAM CODE
Start:
; Loading the divident and the divisor
movlw .100
movwf X_IntL
movlw .34
movwf Y
Main
Div16by8to16_16
clrf X_FracL
clrf X_FracH
movlw 16
movwf Counter
movf Y, w ;keep Y value in accumulator
clrf Y ;and use Y register as temporary
;Find integer part
Div16by8to16_16a
rlf X_IntL, f ;shift next msb into temporary
rlf X_IntH, f
rlf Y, f
rlf Counter, f ;carry has 9th bit of temporary
;copy carry to counter
subwf Y, f ;substract Y (in w) from temporary
skpnc ;if no borrow, set Counter.0
bsf Counter, 0
btfss Counter, 0 ;if Counter.0 clear (borrow) restore temporary
addwf Y, f
clrc ;restore counter
rrf Counter, f
;at this point carry is the next bit of result
decfsz Counter, f ;repeat 16 times to find integer part
goto Div16by8to16_16a
;shift last integer bit
rlf X_IntL, f
rlf X_IntH, f
;goto $
;Find fractional part
bsf Counter, 4 ;Counter = 16
Div16by8to16_16b
;Shift zero bit into temporary
rlf X_FracL, f
rlf X_FracH, f
rlf Y, f
rlf Counter, f ;carry has 9th bit of temporary
;copy carry to counter
subwf Y, f ;substract Y(in w) from temporary
skpnc ;if no borrow, set Counter.0
bsf Counter, 0
btfss Counter, 0 ;if Counter.0 clear (borrow) restore temporary
addwf Y, f
clrc ;restore counter
rrf Counter, f
decfsz Counter, f ;repeat 16 times
goto Div16by8to16_16b
;shift last fractional bit
rlf X_FracL, f
rlf X_FracH, f
movwf Y ;restore divisor
;return
goto $
END ; directive 'end of program'
+
I've tried the 16bits by 8 bits with Q16.16 divide code running base on 16F873. The Integer seems to be ok however what answer should i expect from the fractional part. Is it a fractinal value or remainder
Nikolai Golovchenko answers:
You should expect the fractional part to be just that - the fractional
part, it is not a remainder. This is a binary representation of fixed
point numbers, where the highest bit (bit15) weight equals 1/2, bit14
= 1/4, bit13 = 1/8, ..., bit0 = 1/65536.
A few examples:
.0000 0000 0000 0000b = 0d
.0000 0000 0000 0001b = 1/65536d ~= 0.00001526d
.0000 0000 0000 0010b = 1/32768d ~= 0.00003052d
.0000 0000 0000 0011b = 1/65536d + 1/32768d ~= 0.00004578d
.0000 0000 0000 0100b = 1/16384d
...
.1111 1111 1111 1111b = 1/65536d + 1/32768d + ... + 1/2d =
= 65535 / 65536 ~= 0.9999847d
You can convert it to decimal by simply dividing X_Frac by 65536. The
full division result is:
X_Int + X_Frac/65536
For example:
X_Int = 103
Y = 2
Answer (X_Int/Y): X_Int = 51, X_Frac=32768. In binary:
0000 0000 0011 0011 . 1000 0000 0000 0000
\_____ X_Int______/ \_____ X_Frac ____/
Or, 32+16+2+1+1/2=51.5
| file: /Techref/microchip/math/div/16by8lzf-ng.htm, 8KB, , updated: 2021/3/19 17:59, local time: 2024/12/22 20:01,
owner: NG--944,
3.138.179.120:LOG IN
|
| ©2024 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions? <A HREF="http://sxlist.com/techref/microchip/math/div/16by8lzf-ng.htm"> PIC Microcontoller Math Method Division 16 bits by 8 with result as fraction rather than remainder </A> |
| Did you find what you needed? |
Welcome to sxlist.com!sales, advertizing, & kind contributors just like you! Please don't rip/copy (here's why Copies of the site on CD are available at minimal cost. |
Welcome to sxlist.com! |
.