PICMicrocontollerMathMethod

Scale 8 bits to a percent

;*******************************************************************

```;scale_hex2dec
;  The purpose of this routine is to scale a hexadecimal byte to a
;decimal byte. In other words, if 'h' is a hexadecimal byte then
;the scaled decimal equivalent 'd' is:
;    d = h * 100/256.
;Note that this can be simplified:
;    d = h * 25 / 64 = h * 0x19 / 0x40
;Multiplication and division can be expressed in terms of shift lefts
;and shift rights:
;    d = [ (h<<4) + (h<<3) + h ] >> 6
;The program divides the shifting as follows so that carries are
automatically
;taken care of:
;    d =   (h + (h + (h>>3)) >> 1) >> 2
;
;Inputs:   W - should contain 'h', the hexadecimal value to be scaled
;Outputs:  W - The scaled hexadecimal value is returned in W
;Memory:   temp
;Calls:    none

scale_hex2dec

MOVWF   temp        ;Hex value is in W.
CLRC                ;Clear the Carry bit so it doesn't affect RRF

;Nikolai Golovchenko says: For better precision (especially for higher
;values of input byte), one more term should be added, so that
;d  = (((h >> 3 + h) >> 3 + h) >> 1 + h) >> 2 = h * (1/4 + 1/8 + 1/64 + 1/512)
;
;This adds only 6 cycles, and reduces errors from 51 to 11 cases per
;all combinations of input (in both routines absolute errors are small,+-1).
;
;      RRF     temp,F
;      CLRC
;      RRF     temp,F
;      CLRC
;      RRF     temp,F

RRF     temp,F
CLRC
RRF     temp,F
CLRC
RRF     temp,F      ;temp = h>>3
ADDWF   temp,F      ;temp = h + (h>>3)
RRF     temp,F      ;temp = (h + (h>>3)) >> 1
ADDWF   temp,F      ;temp = h + ((h + (h>>3)) >> 1)
RRF     temp,F
CLRC
RRF     temp,W      ;d = W = (h + (h + (h>>3)) >> 1) >> 2

RETURN

```

 file: /Techref/microchip/math/scale/8bxpercent.htm, 2KB, , updated: 2000/2/25 12:01, local time: 2018/9/26 08:41, TOP NEW HELP FIND:  54.198.23.251:LOG IN

 ©2018 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?Please DO link to this page! Digg it! / MAKE! /  PIC Microcontoller Math Method

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.

Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
 Did you find what you needed? "No. I'm looking for: " "No. Take me to the search page." "No. Take me to the top so I can drill down by catagory" "No. I'm willing to pay for help, please refer me to a qualified consultant" "No. But I'm interested. me at when this page is expanded."

 PICList 2018 contributors: o List host: MIT, Site host massmind.org, Top posters @20180926 RussellMc, Van Horn, David, Sean Breheny, David C Brown, Bob Blick, Isaac M. Bavaresco, Neil, Denny Esterline, Harold Hallikainen, John Gardner, * Page Editors: James Newton, David Cary, and YOU! * Roman Black of Black Robotics donates from sales of Linistep stepper controller kits. * Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters. * Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated! * Contributors: Richard Seriani, Sr.

.