Messages in this thread | | | From | Rikard Falkeborn <> | Date | Wed, 3 Jun 2020 23:53:14 +0200 | Subject | Re: [PATCH v7 1/4] bitops: Introduce the the for_each_set_clump macro |
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On Wed, Jun 03, 2020 at 11:49:37AM +0300, Andy Shevchenko wrote: > On Tue, Jun 2, 2020 at 10:01 PM Rikard Falkeborn > <rikard.falkeborn@gmail.com> wrote: > > On Mon, Jun 01, 2020 at 11:33:30AM +0300, Andy Shevchenko wrote: > > > On Mon, Jun 01, 2020 at 12:37:16AM +0200, Rikard Falkeborn wrote: > > > > On Sun, May 31, 2020 at 02:00:45PM +0300, Andy Shevchenko wrote: > > ... > > > > > If we cast to int, we don't need to worry about the signedness. If > > > > someone enters a value that can't be cast to int, there will still > > > > be a compiler warning about shift out of range. > > > > > > If the argument unsigned long long will it be the warning (it should not)? > > > > No, there should be no warning there. > > > > The inputs to GENMASK() needs to be between 0 and 31 (or 63 depending on the > > size of unsigned long). For any other values, there will be undefined behaviour, > > since the operands to the shifts in __GENMASK will be too large (or negative). > > What I'm implying here that argument may be not constant, and compiler > can't know their values at hand. > So, in the following snippet > > foo(unsigned long long x) > { > u32 y; > y = GENMASK(x, 0); > } > > when you cast x to int wouldn't be a warning of possible value > reduction (even if we know that it won't be higher than 63/31)?
Got it, no I was unable to trigger any warnings like that (but I still can't reproduce to original warning, so take that with a grain of salt). I'd be very surprised if compilers warned for explicit casts but I'll send a proper patch soon to let the build robot try it.
Rikard > > -- > With Best Regards, > Andy Shevchenko
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