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From: Geoff Bull <geoff@research.canon.com.au>
Subject: Re: C/C++ programmer giving Ada95 a chance -- writing an emulator.
Date: 2000/03/28
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To: jross <rem.jross@rem.codemecca.com>
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jross wrote:
> 
> C/C++ is prime for such a low level application.  How about Ada?

Anything you can write in C you can more or less directly translate to Ada.


> My first question is how do you define and write a dispatching
> mechanism as you would in C++ using function pointers in a table for
> execution speed efficiency,  like this:
>

The following is a direct translation of your code:

with Ada.Text_IO; use  Ada.Text_IO;

procedure Example is

   type Opcode is range 16#00# .. 16#FF#;

   type Func_Access is access procedure;

   type Op_Struct is
      record
         Byte : Opcode;
         Func : Func_Access;
      end record;

   procedure Op_U is begin Put_Line ("undefined opcode"); end Op_U;
   procedure Op_00 is begin Put_Line ("opcode 00"); end Op_00;
   procedure Op_01 is begin Put_Line ("opcode 01"); end Op_01;
   procedure Op_02 is begin Put_Line ("opcode 02"); end Op_02;
   procedure Op_03 is begin Put_Line ("opcode 03"); end Op_03;

  Op_Table : array (Opcode) of Op_Struct
    := ((16#00#, Op_00'Access),
        (16#01#, Op_01'Access),
        (16#02#, Op_02'Access),
        (16#03#, Op_03'Access),
        others => (16#FF#, Op_U'Access)
        );

  Core : array (Natural range <>) of Opcode := (0, 1, 2, 3, 55);
  IR : Opcode;

begin

   for PA in Core'Range loop
      IR := Core (PA);
      Op_Table (IR).Func.all;
   end loop;

end Example;