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/* $OpenBSD: _atomic_lock.c,v 1.1 1998/11/20 11:15:35 d Exp $ */
/* Atomic lock for alpha */
#include "spinlock.h"
register_t
_atomic_lock(volatile register_t * lock)
{
register_t old;
register_t new;
int success;
do {
/* load the value of the thread-lock (lock mem on load) */
__asm__( "ldq_l %0, %1" : "=r"(old) : "m"(*lock) );
if (old)
new = old; /* in-use: put it back */
else
new = 1; /* free: store a 1 in the lock */
success = 0;
/* store the new value of the thrd-lock (unlock mem on store) */
/*
* XXX may need to add large branch forward for main line
* branch prediction to be right :(
*/
__asm__( "stq_c %2, %0; beq %2, 1f; mov 1,%1; 1:"
: "=m"(*lock), "=r"(success)
: "r"(new) );
} while (!success);
return old;
}
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