Date: Mon, 30 Jan 2006 20:22:05 +1100 From: Peter Jeremy <peterjeremy@optushome.com.au> To: Scott Long <scottl@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/kern kern_rwlock.c Message-ID: <20060130092205.GB702@turion.vk2pj.dyndns.org> In-Reply-To: <200601292048.k0TKmPSM000635@repoman.freebsd.org> References: <200601292048.k0TKmPSM000635@repoman.freebsd.org>
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On Sun, 2006-Jan-29 20:48:25 +0000, Scott Long wrote:
> gcc can't
> figure out the order of operations at line 519, and neither can I, but this
> is my best guess. Also correct a number of typos and syntax errors.
>
> Revision Changes Path
> 1.3 +4 -4 src/sys/kern/kern_rwlock.c
- if (rw->rw_lock == RW_UNLOCKED ||
- !(rw->rw_lock & RW_LOCK_READ) && (what == RW_RLOCKED ||
- RW_OWNER(rw) != (uintptr_t)curthread))
is perfectly well defined in C. Simplifying names/macros/casts:
if (a == b || !(a & c) && (d == e || f != g))
(partial) precedence rules from operator(7):
() [] -> . left to right
! ~ ++ -- - (type) * & sizeof right to left
== != left to right
& left to right
&& left to right
|| left to right
parenthesising to avoid the bottom 4 precedence rules:
if ((a == b) || (!(a & c) && ((d == e) || (f != g))))
Note that this is different to your patch:
+ if ((rw->rw_lock == RW_UNLOCKED ||
+ !(rw->rw_lock & RW_LOCK_READ)) && (what == RA_RLOCKED ||
+ (rw_owner(rw) != curthread)))
which turns into:
if ((a == b || !(a & c)) && (d == e || (f != g)))
If it's just a matter of silencing gcc, I believe that what is wanted
is (with grouping wraps and indents):
* if (rw->rw_lock == RW_UNLOCKED ||
* (!(rw->rw_lock & RW_LOCK_READ) &&
* (what == RW_RLOCKED || rw_owner(rw) != curthread)))
Note that the behaviour in 1.2 and 1.3 is different if
(rw->rw_lock == RW_UNLOCKED)
--
Peter Jeremy
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