On Thu, 2019-12-05 at 16:30 -0600, Bjorn Helgaas wrote: > You got the "n" on "down" in the subject, but still missing "of" ;) Yes, sorry about that, I tend to re-read what I meant to say instead of what it's actually written. > On Tue, Dec 03, 2019 at 12:47:40PM +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. It turns > > out ilog2() already handles 32/64bit calculations properly, and being > > the building block to the round functions we can rework them as a > > wrapper around it. > > Missing "of" in the function names here. > s/a wrapper/wrappers/ Noted > IIUC the point of this is that roundup_pow_of_two() returned > "unsigned long", which can be either 32 or 64 bits (worth pointing > out, I think), and many callers need something that returns > "unsigned long long" (always 64 bits). I'll update the commit message to be a more explicit. > It's a nice simplification to remove the "__" variants. Just as a > casual reader of this commit message, I'd like to know why we had both > the roundup and the __roundup versions in the first place, and why we > no longer need both. So, the commit that introduced it (312a0c170945b) meant to use the '__' variant as a helper, but, due to the fact this is a header file, some found it and made use of it. I went over some if the commits introducing '__' usages and none of them seem to acknowledge its use as opposed to the macro version. I think it's fair to say it's a case of cargo-culting. > > -#define roundup_pow_of_two(n) \ > > -( \ > > - __builtin_constant_p(n) ? ( \ > > - (n == 1) ? 1 : \ > > - (1UL << (ilog2((n) - 1) + 1)) \ > > - ) : \ > > - __roundup_pow_of_two(n) \ > > - ) > > +#define roundup_pow_of_two(n) \ > > +( \ > > + (__builtin_constant_p(n) && ((n) == 1)) ? \ > > + 1 : (1ULL << (ilog2((n) - 1) + 1)) \ > > +) > > Should the resulting type of this expression always be a ULL, even > when n==1, i.e., should it be this? > > 1ULL : (1ULL << (ilog2((n) - 1) + 1)) \ > > Or maybe there's no case where that makes a difference? It should be 1ULL on either case. Regards, Nicolas
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