[PATCH] Atomic swap and test-and-set

[Jung-uk Kim]

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The attached patch implements atomic_swap_<type>() and
atomic_testandset_<type>() for x86.  <type> is int or long ATM.

The semantics of each operation (in atomic(9) style):

atomic_swap(p, v)
	r = *p;
	*p = v;
	return (r);

atomic_testandset(p, s)
	v = (<type>)1 << s % (sizeof(<type>) * NBBY);
	r = (*p & v) != 0;
	*p |= v;
	return (r);

Note atomic_readandclear_<type>() is now obsolete and implemented as a
macro around atomic_swap_<type>() where the new value v is 0.

Please let me know if you have any objection.

Thanks!

Jung-uk Kim

* Note 1: This patch is also available from here.

http://people.freebsd.org/~jkim/atomic.diff

* Note 2: These atomic ops are useful for porting Linux drivers and it
may simplify diffs, e.g., drm2 for AMD GPUs project.  Currently, I am
using the following wrapper:

http://people.freebsd.org/~jkim/drm_atomic.h

A full patch against kms-radeon tree is here:

http://people.freebsd.org/~jkim/drm_atomic.diff
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