* 0 bit shift
@ 2017-03-29 22:59 Tobin C. Harding
2017-03-29 23:57 ` valdis.kletnieks at vt.edu
0 siblings, 1 reply; 3+ messages in thread
From: Tobin C. Harding @ 2017-03-29 22:59 UTC (permalink / raw)
To: kernelnewbies
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
thanks,
Tobin.
^ permalink raw reply [flat|nested] 3+ messages in thread
* 0 bit shift
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
0 siblings, 1 reply; 3+ messages in thread
From: valdis.kletnieks at vt.edu @ 2017-03-29 23:57 UTC (permalink / raw)
To: kernelnewbies
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)
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^ permalink raw reply [flat|nested] 3+ messages in thread
* 0 bit shift
2017-03-29 23:57 ` valdis.kletnieks at vt.edu
@ 2017-03-30 0:39 ` Tobin C. Harding
0 siblings, 0 replies; 3+ messages in thread
From: Tobin C. Harding @ 2017-03-30 0:39 UTC (permalink / raw)
To: kernelnewbies
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.
^ permalink raw reply [flat|nested] 3+ messages in thread
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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
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