From: "Etienne Lorrain" <etienne_lorrain@yahoo.fr>
To: gcc@gcc.gnu.org
Subject: Re: How to change bit-field allocation
Date: Tue, 07 Sep 2004 14:59:00 -0000 [thread overview]
Message-ID: <20040907145951.77752.qmail@web11802.mail.yahoo.com> (raw)
Min ZOU wrote:
> Robert Dewar wrote:
> > I guess that the problem is that he wants a magical way of dealing with
> > endian differences between processors. Many people want this, but
> > unfortunately there is no coherent consistent way of doing this.
> > This topic has been much studied and discussed in the Ada world :-)
>
> The problem is not due to endian differences but compiler differences. I >
came across this problem when I have to combine two binary images while
> are compiled by different compilers: one by GCC, the other by SH
> proprietary compiler. However the bit-field's members are allocated from
> the lower bit in GCC, while from higher bit in SH compiler.
I had the impression that only one logical way was possible depending
on the processor, so that:
union {
unsigned char val1;
unsigned val2 : 8;
unsigned char val3[1];
struct { unsigned char c1, c2; } val3;
... whatever ...
} a_union;
the value of "a_union.val1", "a_union.val2", "a_union.val3[0]" and
"a_union.val3.c1" are identical - assuming 8 bits chars.
Same for (assuming 16 bits shorts):
union {
unsigned short val1;
unsigned val2 : 16;
enum { e1, e2, e3 } val3 : 16;
} union2;
Etienne.
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next reply other threads:[~2004-09-07 14:59 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-07 14:59 Etienne Lorrain [this message]
-- strict thread matches above, loose matches on Subject: below --
2004-09-06 11:41 Min ZOU
2004-09-06 17:15 ` Ramana Radhakrishnan
2004-09-06 21:43 ` James E Wilson
2004-09-06 22:19 ` Robert Dewar
2004-09-07 3:44 ` Min ZOU
2004-09-07 15:56 ` Dave Korn
2004-09-13 9:09 ` tm_gccmail
2004-09-07 1:24 ` DJ Delorie
2004-09-07 3:47 ` Min ZOU
2004-09-07 14:07 ` Robert Dewar
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