On Tue, 2011-07-26 at 01:07 -0700, Nicholas A. Bellinger wrote:
> On Tue, 2011-07-26 at 00:53 -0700, Joe Perches wrote:
> > On Tue, 2011-07-26 at 07:10 +0000, Nicholas A. Bellinger wrote:
> > > Add new DIV_ROUND_UP_ULL macro usage for 32-bit architectures requiring
> > > unsigned long long division of sectors * dev_max_sectors.
> > []
> > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > []
> > > +#define DIV_ROUND_UP_ULL(ll,d) \
> > > + ({ unsigned long long _tmp = (ll)+(d)-1; do_div(_tmp, d); _tmp; })
> > Maybe use uint64_t and a temporary for d?
> > #define DIV_ROUND_UP_ULL(ll, d) \
> > ({ \
> > typeof(d) _d = d; \
> > uint64_t _tmp = (uint64_t)(ll) + _d - 1; \
> > do_div(_tmp, _d); \
> > _tmp; \
> > })
> Hi Joe,
Hi Nicholas.
> Not sure on this one myself.. Would this case ever be strictly required
> for proper 32-bit operation with unsigned long long division with
> sector_t..?
It's just for correctness.
For 32 bit uses, if ll is a unsigned long and not an
unsigned long long then without the cast the addition
will be done as a 32 bit value.
e.g.:
$ cat t.c
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char** argv)
{
unsigned long l = 0xFFFFFFFFUL;
unsigned long long ull = l + 1;
unsigned long long ull2 = (unsigned long long)l + 1;
printf("l: %lu, ull:%llu, ull2: %llu\n", l, ull, ull2);
}
$ gcc t.c
$ ./a.out
l: 4294967295, ull:0, ull2: 4294967296
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