From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,53a810f13e8ba40
X-Google-Attributes: gid103376,public
From: mheaney@ni.net (Matthew Heaney)
Subject: Re: Byte/Bit Twiddling in Ada
Date: 1997/02/14
Message-ID: <mheaney-ya023680001402972052280001@news.ni.net>#1/1
X-Deja-AN: 218920054
References: <5dvfnn$olj@neocad.xilinx.com>
Content-Type: text/plain; charset=ISO-8859-1
Organization: Estormza Software
Mime-Version: 1.0
Newsgroups: comp.lang.ada
Date: 1997-02-14T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <5dvfnn$olj@neocad.xilinx.com>, kruse@xilinx.com (Jim Kruse) wrote:


>Is there any portable way to do byte and bit manipulation in Ada, on a
>long word?  I found no mention of this topic in the FAQ.

Yes.  It may be that using Unchecked_Conversion is called for.

On the other hand, if you're on a UNIX box you may be able to bind to
htons, for example.

>
>My friend is trying to write some code that does byte swapping,
>presumably to handle conversions to and from IEEE number formats.

Well, here's an example of byte-swapping a longword (32 bits) that uses
Unchecked_Conversion.  Note also that bit manipulation is fully supported
in Ada; see the package Interfaces.

type Byte is new Integer_8;
type Byte_Array is array (Positive range <>) of Byte;

subtype Longword_As_Byte_Array is Byte_Array (1 .. 4);

function To_Byte_Array is 
   new Unchecked_Conversion (
      Source => Integer_32, 
      Target  => Longword_As_Byte_Array);

function To_Longword is
   new Unchecked_Conversion (
      Source => Longword_As_Byte_Array,
      Target => Integer_32);

function Byte_Swapped (O : Integer_32) return Integer_32 is
   The_Byte_Array : Longword_As_Byte_Array :=
      To_Byte_Array (O);
begin
   The_Byte_Array := 
      The_Byte_Array (4) &
      The_Byte_Array (3) &
      The_Byte_Array (2) &
      The_Byte_Array (1);

   return To_Longword (The_Byte_Array);
end;

--------------------------------------------------------------------
Matthew Heaney
Software Development Consultant
<mailto:matthew_heaney@acm.org>
(818) 985-1271