Messages in this thread | | | Subject | Re: [PATCH] drivers/staging/wilc1000: fix sparse warning: right shift by bigger than source value | From | Rui Teng <> | Date | Wed, 12 Jul 2017 10:23:02 +0800 |
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On 12/07/2017 1:04 AM, Greg Kroah-Hartman wrote: > On Mon, Jul 10, 2017 at 04:57:31PM +0800, Rui Teng wrote: >> This patch sets memory to zero directly to avoid unnecessary shift and >> bitwise operations on bool type, which can fix a sparse warning and also >> improve performance. > > It does? How did you measure the performance impact? What was now > faster?
It can avoid 3 times right shift and 3 times bitwise operations. And once memory set should also faster than 4 times copy operations. And add number 4 once should also faster than 4 times plus plus.
> > thanks, > > greg k-h > > >> >> Signed-off-by: Rui Teng <rui.teng@linux.vnet.ibm.com> >> --- >> drivers/staging/wilc1000/host_interface.c | 7 +++---- >> 1 file changed, 3 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/staging/wilc1000/host_interface.c b/drivers/staging/wilc1000/host_interface.c >> index 2568dfc15181..036c5c19a016 100644 >> --- a/drivers/staging/wilc1000/host_interface.c >> +++ b/drivers/staging/wilc1000/host_interface.c >> @@ -2416,10 +2416,9 @@ static void Handle_SetMulticastFilter(struct wilc_vif *vif, >> goto ERRORHANDLER; >> >> pu8CurrByte = wid.val; >> - *pu8CurrByte++ = (strHostIfSetMulti->enabled & 0xFF); >> - *pu8CurrByte++ = ((strHostIfSetMulti->enabled >> 8) & 0xFF); >> - *pu8CurrByte++ = ((strHostIfSetMulti->enabled >> 16) & 0xFF); >> - *pu8CurrByte++ = ((strHostIfSetMulti->enabled >> 24) & 0xFF); >> + memset(pu8CurrByte, 0, 4); >> + *pu8CurrByte = (strHostIfSetMulti->enabled & 0xFF); >> + pu8CurrByte += 4; > > Are you sure enabled isn't larger than 8 bits?
The size of bool may larger than 8 bits. But when we assign any value to bool type, the value of bool type will only be 1 or 0. For example, the following output will be 1 other than 0x100. bool b = 0x100; printf("b: %d\n", b);
Or I think it should change 'enabled' type from bool to u32, to make sure that the right shift operation can take effect.
> > thanks, > > greg k-h >
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