Date: Thu, 7 Aug 2003 09:43:18 -0400 (EDT) From: Daniel Eischen <eischen@vigrid.com> To: alpha@freebsd.org Subject: Atomic swap Message-ID: <Pine.GSO.4.10.10308070941260.2511-100000@pcnet5.pcnet.com>
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[ I'm not subscribed to alpha@; please keep me on the CC ]
I need an atomic swap function for libpthread. Here's my hack
of an implementation:
/*
* Atomic swap:
* Atomic (tmp = *dst, *dst = val), then *res = tmp
*
* void atomic_swap_long(long *dst, long val, long *res);
*/
static __inline
void atomic_swap_long(volatile long *dst, long val, long *res)
{
u_int64_t result;
__asm __volatile (
"1:\tldq_l %0,%1\n\t"
"stq_c %2,%1\n\t"
"beq %2,2f\n\t" /* Why is this beq instead of bne 1b? */
"br 3f\n"
"2:\tbr 1b\n"
"3:\n"
: "=&r" (result)
: "m" (*dst), "r" (val)
: "memory");
*res = result;
}
As annotated above, there seems to be one more branch than
necessary.
Can someone look this over for me? I really don't quite
know what I'm doing when it comes to inline assembly.
--
Dan Eischen
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