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Date: Fri, 10 Mar 2017 08:32:41 -0600
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe LEROY <christophe.leroy@c-s.fr>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
 Benjamin Herrenschmidt <benh@kernel.crashing.org>,
 Paul Mackerras <paulus@samba.org>, Scott Wood <oss@buserror.net>,
 linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc: sysdev: cpm1: Optimise gpio bit calculation
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On Fri, Mar 10, 2017 at 03:04:48PM +0100, Christophe LEROY wrote:
> Le 10/03/2017 à 14:06, Segher Boessenkool a écrit :
> >On Fri, Mar 10, 2017 at 11:54:19AM +0100, Christophe LEROY wrote:
> >>gpio_get() and gpio_set() are used extensively by some GPIO based
> >>drivers like SPI, NAND, so it may be worth it as it doesn't impair
> >>readability (if anyone prefers, we could write  (1 << 31) >> i  instead
> >>of  0x80000000 >> i )
> >
> >1 << 31 is undefined behaviour, of course.
> >
> 
> Shall it be 1U << 31 ?

Sure, that works.  "1 << (31 - i)" is most readable (but it doesn't yet
generate the code you want).


Segher