Re: fcntl error

[David Howells]

Linus Torvalds <torvalds@xxxxxxxx> wrote:
> That implies that while non-zero for "set" is ok, that non-zero had better
> have the _low_ bits set. Which is not true on architectures that use just
> a logical and with the bits in the word.
> 
> Which implies that FD_ISSET() really must NOT be of that "logical and" 
> approach, which in turn implies that it should be either a inequality 
> expression, or it should be a "shift down and then and with 1".

Or maybe:

#define	__FD_ISSET(d, set)	(!!((set)->fds_bits[__FDELT(d)] & __FDMASK(d)))

Which is probably better than a shift and bit-and. That then leaves it up to
the compiler as to whether the generation of 0 or 1 is actually necessary
(which if isn't if it's just the condition in an if-statement).

Or even:

#define FD_ISSET(fd,fdsetp)	(!!__FD_ISSET(fd,fdsetp))

Which would then apply to all arch's regardless.

David
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