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From: "Eric G. Miller" <egm2@jps-nospam.net>
Subject: Re: Last stream problem: byte order
Newsgroups: comp.lang.ada
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X-Comment-To: "Dr. Michael Paus" <paus@ib-paus.com>
Date: Thu, 28 Mar 2002 02:24:57 GMT
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In <3CA20BAA.FD53C08A@ib-paus.com>, Dr. Michael Paus wrote:

> Erik Sigra schrieb:
>> 
>> tisdagen den 26 mars 2002 11.25 skrev du:
>> > If you also check the byte order of your system at runtime (there is a
>> > system constant in Ada which you can check) you can even achieve the effect
>> > that all stream data is always written in network byte order independent of
>> > the platform your program is running on.
>> 
>> Why runtime check? Compile time check seems more reasonable to me. Or can the
>> same compiled program really run on architectures with different endiannes?
> 
> It depends on how clever the compiler is. If the compiler optimizes the
> static expression in the following if-statement away then it is indeed a
> compile time check. Otherwise it is a run-time check.
> 
>       if System.Default_Bit_Order = System.Low_Order_First then
>          ... (swap the bytes)
>       else
>          ... (don't swap the bytes)
>       end if;
> 
> But I don't think this makes a big difference in either case.

GNAT gives a warning that the condition is always true (or false).  Don't know
if it eliminates the unreachable branch (I would think so with -02).  Resorting
to preprocessing trickery would probably insure it is always a compile time
check.  Don't know if there's another way...