On Wed, 2019-11-27 at 18:06 +0000, Robin Murphy wrote: > On 26/11/2019 12:51 pm, Leon Romanovsky wrote: > > On Tue, Nov 26, 2019 at 10:19:39AM +0100, Nicolas Saenz Julienne wrote: > > > Some users need to make sure their rounding function accepts and returns > > > 64bit long variables regardless of the architecture. Sadly > > > roundup/rounddown_pow_two() takes and returns unsigned longs. Create a > > > new generic 64bit variant of the function and cleanup rougue custom > > > implementations. > > > > Is it possible to create general roundup/rounddown_pow_two() which will > > work correctly for any type of variables, instead of creating special > > variant for every type? > > In fact, that is sort of the case already - roundup_pow_of_two() itself > wraps ilog2() such that the constant case *is* type-independent. And > since ilog2() handles non-constant values anyway, might it be reasonable > to just take the strongly-typed __roundup_pow_of_two() helper out of the > loop as below? > > Robin > That looks way better that's for sure. Some questions. > ----->8----- > diff --git a/include/linux/log2.h b/include/linux/log2.h > index 83a4a3ca3e8a..e825f8a6e8b5 100644 > --- a/include/linux/log2.h > +++ b/include/linux/log2.h > @@ -172,11 +172,8 @@ unsigned long __rounddown_pow_of_two(unsigned long n) > */ > #define roundup_pow_of_two(n) \ > ( \ > - __builtin_constant_p(n) ? ( \ > - (n == 1) ? 1 : \ > - (1UL << (ilog2((n) - 1) + 1)) \ > - ) : \ > - __roundup_pow_of_two(n) \ > + (__builtin_constant_p(n) && (n == 1)) ? \ > + 1 : (1UL << (ilog2((n) - 1) + 1)) \ Then here you'd have to use ULL instead of UL, right? I want my 64bit value everywhere regardless of the CPU arch. The downside is that would affect performance to some extent (i.e. returning a 64bit value where you used to have a 32bit one)? Also, what about callers to this function on platforms with 32bit 'unsigned longs' that happen to input a 64bit value into this. IIUC we'd have a change of behaviour. Regards, Nicolas
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