From: me@tobin.cc (Tobin C. Harding)
To: kernelnewbies@lists.kernelnewbies.org
Subject: 0 bit shift
Date: Thu, 30 Mar 2017 11:39:16 +1100 [thread overview]
Message-ID: <20170330003916.GJ25014@eros> (raw)
In-Reply-To: <59220.1490831870@turing-police.cc.vt.edu>
On Wed, Mar 29, 2017 at 07:57:50PM -0400, valdis.kletnieks at vt.edu wrote:
> On Thu, 30 Mar 2017 09:59:44 +1100, "Tobin C. Harding" said:
> > What is the reason for the zero bit shift in this code please?
> >
> > #define SDIO_STATE_PRESENT (1<<0) /* present in sysfs */
> >
> > file: include/linux/mmc/sdio_func.h
>
> Most likely, to indicate that it's a bitmask in the 'unsigned int state'
> in the line above, rather than an integer.
>
> See the other 2 uses of the flag in-tree:
>
> [/usr/src/linux-next] git grep SDIO_STATE_PRESENT
> include/linux/mmc/sdio_func.h:#define SDIO_STATE_PRESENT (1<<0) /* present in sysfs */
> include/linux/mmc/sdio_func.h:#define sdio_func_present(f) ((f)->state & SDIO_STATE_PRESENT)
> include/linux/mmc/sdio_func.h:#define sdio_func_set_present(f) ((f)->state |= SDIO_STATE_PRESENT)
>
Awesome, thanks.
prev parent reply other threads:[~2017-03-30 0:39 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-29 22:59 0 bit shift Tobin C. Harding
2017-03-29 23:57 ` valdis.kletnieks at vt.edu
2017-03-30 0:39 ` Tobin C. Harding [this message]
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