Re: ESP code rewritten in Ada

[guerby@gnat.com (Laurent Guerby)]

>-- General-purpose low-pass filter,
>-- implementing a first-order lag.
>-- Instantiate a copy for each input
>-- such that copy has same lifetime
>-- as input.
>generic
>  Shift : Positive;
>  -- Gain is 2 to the negative Shift.
>  -- E.g., shift => 4 implies gain = 1/16
>  -- 2**Shift must fit in max precision
>
>  type Signal is range <>;
>  -- Signal should be at least Shift+1
>  -- bits less than max precision
>
>package Filter is
>  function Lag (U : Signal) return Signal;

   I would add a pragma Inline here, so the generated code may look
even more competitive ;-).

>end Filter;
>
>with System;
>package body Filter is
>
>  type Long is range
>    System.Min_Int .. System.Max_Int;

   This may drag unreasonable arithmetic on a given machine.  May be
it's better to add a "base" type to the generic formal (type Long is
range <>). Or to compute the needed range:

   type Long is range 0 .. 2 ** Shift;

   But this may damage compiler optimization.

>  X : Long := 0;
>
>  function Lag (U : Signal) return Signal is
>    D : constant Long := Long(2**Shift);
>  begin
>    X := X + Long(U) - X / D;
>    return Signal (X / D);
>  end Lag;
>
>end Filter;





-- 
Laurent Guerby <guerby@gnat.com>, Team Ada.
   "Use the Source, Luke. The Source will be with you, always (GPL)."