Excuse me correct is
0x19 = B00011001 -> 0x18 = 24
24/64 = 3/8  and
d =   (h>>3) + (h>>2)
You may add one time C and error is max 1%




---Justin Crooks <jcrooks@WYOMING.COM> wrote:
>
> ----------
> > From: Scott Dattalo <sdattalo@UNIX.SRI.COM>
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: Re: Conversion of byte to percentage
> > Date: Thursday, May 21, 1998 10:53 AM
> >
> > adrian aslett wrote:
> > >
> > > I have a need to convert a byte value into a percentage. I know
I have
> > > to work with integer values but does anyone know how I should go
about
> > > doing this.
> > >
> > > Any ideas will be appreciated ! !
> >
> > Here's one that'll do it:
> >
> >
> > ;*******************************************************************
> > ;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
> >         RRF     temp,F
> >         CLRC
> >         RRF     temp,F
> >         CLRC
> >         RRF     temp,F          ;temp = h>>3
> >         ADDWF   temp,F          ;temp = h + (h>>3)
> What happens if result > 0xFF?
> >         RRF     temp,F          ;temp = (h + (h>>3)) >> 1
> >         ADDWF   temp,F          ;temp = h + ((h + (h>>3)) >> 1)
> Again, same issue.
> >         RRF     temp,F
> >         CLRC
> >         RRF     temp,W          ;d = W = (h + (h + (h>>3)) >> 1)
>> 2
> >
> >         RETURN
>
> This is excellent, but will not work for values > 64%.  I like how
clean it
> is, though.  You could add a line to check if MSB set.  Subtract 128
if
> set, and add 50% at the end.
>

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