Re: float with 24-bit resolution

["Robert I. Eachus" <rieachus@attbi.com>]

Jeffrey Creem wrote:
> <mailbox@adrianhoe.nospam.com.my> wrote in message
> news:3F3CCB0F.543478AF@adrianhoe.nospam.com.my...
> 
>>Hi,
>>
>>I looked through the LRM and searched CLA but I could not find any
>>solution. Perhaps I've overlook somewhere.
>>
>>I need a float with 24-bit resolution. My data needs to be encoded into
>>24 bits at a scaling of 720 degrees / 2^24 bits with the most
>>significant bit being the sign bit. This results in a value that ranges
>>from +359.9999571 degrees (0x7FFFFF) to -360.0000000 degrees (0x800000)
>>at increments of approximately 4.291534424e-5 degrees per bit.
> 
> 
> This does not sound anything like a float at all. It sounds much more like a
> typical implementation of a fixed point type. Something along the lines of
> 
> package My_Pack is
> 
> The_Delta : constant := 4.291534424e-5;
> 
>   type Probably_Gonna_Work_But_Language_Lawyers_Will_Complain_Type is delta
> The_Delta range - 360.0 .. 359.9999571;
>   for  Probably_Gonna_Work_But_Language_Lawyers_Will_Complain_Type'Small use
> The_Delta;
>   for Probably_Gonna_Work_But_Language_Lawyers_Will_Complain_Type'Size use
> 24;

Okay, I'll complain. ;-)  You can declare the type as

   type Probably_Gonna_Work_But_Language_Lawyers_Will_Complain_Type is 

          delta The_Delta range - 360.0 .. 360.0;

but if you don't want to, you are much more likely to get exactly what 
you want, and have the users understand it as well, if you say:

   The_Delta : constant := 720.0/2**24;

   type Gonna_Work_And_Language_Lawyers_Will_Not_Complain_Type is
          delta The_Delta range - 360.0 .. 360.0 - The_Delta;
   for Gonna_Work_And_Language_Lawyers_Will_Not_Complain_Type'Size
          use 24;



--
                                              Robert I. Eachus

"As far as I'm concerned, war always means failure." -- Jacques Chirac, 
President of France
"As far as France is concerned, you're right." -- Rush Limbaugh