Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH 4/6] Implement a general log2 facility in the kernel | Date | Wed, 13 Sep 2006 17:50:52 +0100 |
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Luck, Tony <tony.luck@intel.com> wrote:
> > This facility provides three entry points: > > > > log2() Log base 2 of u32 > > ll_log2() Log base 2 of u64 > > long_log2() Log base 2 of unsigned long > > The names are rather counter-intuitive. "ll" sounds like "long long", so > why does it opearte on *unsigned* 64-bit? Ditto for "long_log2()". > Perhaps they should be log2_u32(), log2_u64(), etc.
Well, given that you can't represent a log of a negative number, I'm not sure it matters.
Note that long_log2() already exists and is of arch-dependent size.
> Even better if someone can come up with the right pre-processor magic > using sizeof/typeof so that you could just use "log2(any type)"
I then end up with 32 of these per usage if I pass in a definite 32-bit value:
warning: comparison is always false due to limited range of data type
because of the:
n >= (1ULL << 63) ? 63 : \ n >= (1ULL << 62) ? 62 : \ n >= (1ULL << 61) ? 61 : \ ...
in ll_log2().
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