PIC Microcontoller Basic Math Scaleing Methods

• 8 bit to a percentage from Scott Dattalo with optional precision increase from Nikolai Golovchenko
• 8 bit to a percentage fast from Jason Harper
• 8 bit to a percentage accurate from Dmitry Kiryashov

Also:

• The "Bill & Pookie" 10 bit A2D binary to decimal w/scaleing code generator
• Constant Division/Multiplication Code Generator

Code:

• 8-bit value scaled by n-bit fraction

  I have a lookup table with 4-bit numbers m=0..15. A value t should be scaled according to theese numbers, so that

  s = t * m/16
  

  Rather than using 16-bit multiplication followed by s>>4, I found a much faster code. As can be seen, the code can be carried out for e.g. 7-bit m-values as well.

  --------------------
  	clrf s
  	movf t, W
  
  	bcf STATUS, C
  	btfsc m, 0
  	addwf s, F
  	rrf s, F
  
  	bcf STATUS, C
  	btfsc m, 1
  	addwf s, F
  	rrf s, F
  
  	bcf STATUS, C
  	btfsc m, 2
  	addwf s, F
  	rrf s, F
  
  	bcf STATUS, C
  	btfsc m, 3
  	addwf s, F
  	rrf s, F
  
  	btfsc STATUS, C
  	incf s, F		;nearest value
  -----------------------
  

  Regards, Anders Jansson

Comments:

• OK, I realize now that my scaling algorithm is very similar to the 8x8bit mult by Warren. /A.J