linux-kernel - Re: __LITTLE_ENDIAN vs. __LITTLE_ENDIAN

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Message-ID: <m37ilwcc4v.fsf@maximus.localdomain>
Date:	Tue, 09 Oct 2007 21:37:52 +0200
From:	Krzysztof Halasa <khc@...waw.pl>
To:	Timur Tabi <timur@...escale.com>
Cc:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	Anton Altaparmakov <aia21@....ac.uk>,
	Jan Engelhardt <jengelh@...putergmbh.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: __LITTLE_ENDIAN vs. __LITTLE_ENDIAN_BITFIELD

Timur Tabi <timur@...escale.com> writes:

>> There is no such thing as bit-order.
>
> Yes, there is.  You need to read the article at
> http://www.linuxjournal.com/article/6788.  Explains what it means for
> bits to be in one order versus another.  This is from the perspective
> of external devices, not the CPU (which is always consistent with
> regards to bit order)

Have you ever seen a device or platform with the bits reversed?
I.e. one on which 0x01 from CPU POV is 0x80 or 0x80000000 etc.
from device's POV?

Perhaps I was too brief, I should've written "there is no such
thing WRT the CPU-device connections" because the bit order
actually exists on things like serial lines, though it's totally
independent from big/little endianness of the CPU and/or
peripheral devices, and one can't assume anything matches there.

On parallel bus, all bits (at least of an 8-bit byte) are stored
and transmitted at the same time and address, so no bit can be
first or last.

Once again, you shift left (towards MSBit), you multiply, shifting
right divides. At least as long as you limit it to a single byte.

Perhaps if you tell us what are you exactly trying to achieve...
-- 
Krzysztof Halasa
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