Re: [PATCH] asm-generic/bitops/fls64.h

[Nickolay Vinogradov]

Alexander van Heukelum ÐÐÑÐÑ:

> > No.  "fls" is for finding the last set bit in an _int_.  It is not
> > supposed to have random crap passed to it, such as types longer than
> > sizeof(int).
> >
> > If you're going to pass long long (64-bit) arguments to fls, and then
> > cast them to a u32, you're truncating the value, and you'll get the
> > wrong answer if bit 33 or greater is set.  If you don't actually care
> > about the upper bits, don't pass a 64-bit quantity to fls().
> >
> > If you want to use fls with a long long, use fls64 instead.  Or for top
> > marks, use a u64 and fls64.
>
> But that was the problem we began with: the generic fls64 passes an u64
> to fls. Nickolay's original patch solves that by putting a cast to u32
> in fls64. I did not, however, understand why the cast was needed.

The cast was needed because fls is a macro, not a function.

--
Nickolay Vinogradov
Protei Research and Development Center
St.Petersburg, 194044, Russia
Tel.: +7 812 449 47 27
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