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Speed up and explain fd_isset()

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Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
This commit is contained in:
Denys Vlasenko 2013-11-06 11:34:02 +01:00
parent 85db86e6d9
commit 1297a513da
1 changed files with 13 additions and 5 deletions
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18
desc.c
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@ -477,12 +477,20 @@ sys_getdtablesize(struct tcb *tcp)
}
#endif
static int
fd_isset(int d, fd_set *fds)
/* FD_ISSET from libc would abort for large fd if built with
* debug flags/library hacks which enforce array bound checks
* (fd_set contains a fixed-size array of longs).
* We need to use a homegrown replacement.
*/
static inline int
fd_isset(unsigned fd, fd_set *fds)
{
const int bpl = 8 * sizeof(long);
long *s = (long *) fds;
return !!(s[d / bpl] & (1L << (d % bpl)));
/* Using unsigned types to avoid signed divisions and shifts,
* which are slow(er) on many CPUs.
*/
const unsigned bpl = 8 * sizeof(long);
unsigned long *s = (unsigned long *) fds;
return s[fd / bpl] & (1UL << (fd % bpl));
}
static int