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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