Re: Conversion from floating point to signed 16 bits

[Adam Beneschan <adam@irvine.com>]

On May 19, 11:51 am, Olivier Scalbert <olivier.scalb...@algosyn.com>
wrote:
> Hello,
>
> My problem:
> I need to convert an "analogic" value which can vary from 0.0 to 1.0
> into a "discrete" value which is a signed 16 bits integer.
>
> My implementation:
> -----------------------------
> with Ada.Text_IO;
>
> procedure convert is
>      type Analog_Value is digits 10 range 0.0 .. 1.0;
>      type Signed_16    is range -32768 .. 32767;
>      type Unsigned_16  is range      0 .. 65535;
>
>      function Cv(Value: Analog_Value) return Signed_16 is
>          U16: Unsigned_16;
>      begin
>          U16 := Unsigned_16(65535.0 * Value);
>          return Signed_16(U16 - 32768);
>      end Cv;
>
>      procedure Put(S16: Signed_16) is
>      begin
>          Ada.Text_IO.Put_Line(Signed_16'image(S16));
>      end put;
> begin
>     Put(Cv(0.00)); -- Must be -32768
>     Put(Cv(0.25)); -- Must be -16384
>     Put(Cv(0.50)); -- Must be      0
>     Put(Cv(0.75)); -- Must be  16383
>     Put(Cv(1.00)); -- Must be  32767
> end convert;
> -----------------------------
>
> My question:
> Is there an other way to do this in Ada (Representation ? Other parts of
> Ada I do not know ?)

If your problem is that you're getting a Constraint_Error when the
subtraction "U16 - 32768" has a negative result, you can convert U16
to some larger integer type before doing the subtraction:

  return Signed_16(Signed_32(U16) - 32768);

                              -- Adam