Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH 09/17] m68k: Implement xor_unlock_is_negative_byte | Date | Tue, 19 Sep 2023 15:22:25 +0000 |
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From: Matthew Wilcox <willy@infradead.org> > Sent: 19 September 2023 16:15 > > On Tue, Sep 19, 2023 at 02:35:25PM +0000, David Laight wrote: > > From: Matthew Wilcox <willy@infradead.org> > > > Sent: 19 September 2023 15:26 > > > > > > On Tue, Sep 19, 2023 at 01:23:08PM +0000, David Laight wrote: > > > > > Well, that sucks. What do you suggest for Coldfire? > > > > > > > > Can you just do a 32bit xor ? > > > > Unless you've got smp m68k I'd presume it is ok? > > > > (And assuming you aren't falling off a page.) > > > > > > Patch welcome. ... > I have a 68020 book; what I don't have is a Coldfire manual. > > Anyway, that's not the brief. We're looking to (eg) clear bit 0 > and test whether bit 7 was set. So it's the sign bit of the byte, > not the sign bit of the int.
Use the address of the byte as an int and xor with 1u<<24. The xor will do a rmw on the three bytes following, but I doubt that matters.
David
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