Volume Conversion

I think you need to reconsider the range you wish to display and send. Every amp I ever owned acted like the heater in your father's first car. Everything happens just to the left of centre and it was impossible to adjust. You never want the extremes. So consider offering 25% to 50% or something like that - experiment to find out.

You also need to consider how many volume steps you need. 25 or 30 seems to be plenty for a typical system, although you may be limited by the range mentioned above. And as you mentioned, you need 2 or 3 bumps on 0..255 to get 1 bump on 0..100.

So 0..255 and 0..100 may not be what you want; maybe you need 25 levels which are hard-coded to send 25..49%, or 20 levels coded to send 30..69%

Here are my general-purpose conversion functions:

(******************************************************************************)
define_function integer AdjustTo255    ( (* Output - Result in range 0 - 255  *)                                                             
   integer nArgValue                   , (* Input  - Value to convert         *)
   integer nArgMinimum                 , (* Input  - Minimum input value      *)
   integer nArgMaximum                 ) (* Input  - Maximum input value      *)
(******************************************************************************)                 
{
return (((nArgValue - nArgMinimum) * 255) / (nArgMaximum - nArgMinimum));
} (* AdjustTo255 *) 

(******************************************************************************)
define_function integer AdjustFrom255  ( (* Output - Result in range as below *)
   integer nArgValue                   , (* Input  - Value in range 0 - 255   *)
   integer nArgMinimum                 , (* Input  - Minimum input value      *)
   integer nArgMaximum                 ) (* Input  - Maximum input value      *)
(******************************************************************************)                 
{
return ((nArgValue * (nArgMaximum - nArgMinimum)) / 255) + nArgMinimum;
} (* AdjustFrom255 *)  

You would call this function like so for the conversion you requested:

nValue0to100 = AdjustFrom255(nValue0to255,0,100)

To use my suggestions above, you would code like this:

nValue25to49 = AdjustFrom255(nValue255,25,49)

If you want to do true rounding on such conversions, don't use integer math on your conversion function: create a temporary DOUBLE, assign the value to that, do your conversion, add .5 to the result, then TYPE_CAST it back to an integer. Especially with things like volume bars, it will make a smoother transition.