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From: dewar@gnat.com
To: dewar@gnat.com, fw@deneb.enyo.de
Subject: Re: Big-endian Gcc on Intel IA32
Cc: gcc@gcc.gnu.org, torvalds@transmeta.com
Message-Id: <20011223145954.15F7EF28C6@nile.gnat.com>
Date: Sun, 23 Dec 2001 07:06:00 -0000
X-SW-Source: 2001-12/txt/msg01248.txt.bz2

<<I wouldn't tackle this problem at the struct level, but at the
discrete type level, IOW introduce additional integer types with
different resentation.  This would already greatly help in many cases.
>>

Yes, I already suggested this, and noted that this was what we did
in Realia COBOL (see archives)

<<If you've got signed-magnitude representation, you've got plenty of
positions in which you can place the sign bit.
>>

There are no S&M machines, so this is bogus. There are 1's complement machines
but the issue is not affected by 1s or 2s complement. Even for S&M, the
sign bit was always the most significant, so you are inventing a non-existant
problem here.

<<If the machine is word-adressed, all we do in this regard won't help
much to increase portability because a lot of data structures with a
given external representation assume you can access individual octets,
and the mapping to a useful machine implementation is certainly not
straightforward.  For example, how does an IP header look on a 36 bit
machine?
>>>

The point is that it is quite straightforward to address the problem WITHIN
an address unit. Ada already does this. Have a look at what GNAT implements
here with the Bit_Order attribute (and also see the discussion of why it
is not easy to do more). This is in the GNAT RM.