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diff --git a/libthreads/i386/cthreads.h b/libthreads/i386/cthreads.h
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+/* 
+ * Mach Operating System
+ * Copyright (c) 1991,1990 Carnegie Mellon University
+ * All Rights Reserved.
+ * 
+ * Permission to use, copy, modify and distribute this software and its
+ * documentation is hereby granted, provided that both the copyright
+ * notice and this permission notice appear in all copies of the
+ * software, derivative works or modified versions, and any portions
+ * thereof, and that both notices appear in supporting documentation.
+ * 
+ * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
+ * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
+ * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
+ * 
+ * Carnegie Mellon requests users of this software to return to
+ * 
+ *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
+ *  School of Computer Science
+ *  Carnegie Mellon University
+ *  Pittsburgh PA 15213-3890
+ * 
+ * any improvements or extensions that they make and grant Carnegie Mellon
+ * the rights to redistribute these changes.
+ */
+/*
+ * HISTORY
+ * $Log:	cthreads.h,v $
+ * Revision 2.7  92/01/03  20:36:59  dbg
+ * 	Add volatile to spin_lock_t.  Change spin_unlock and
+ * 	spin_try_lock definitions back to memory operands, but rely on
+ * 	volatile attribute to keep from using value in memory.
+ * 	[91/09/04            dbg]
+ * 
+ * Revision 2.6  91/08/28  20:18:39  jsb
+ * 	Safer definitions for spin_unlock and spin_try_lock from mib.
+ * 
+ * Revision 2.5  91/07/31  18:36:49  dbg
+ * 	Add inline substitution for cthread_sp, spin_unlock,
+ * 	spin_try_lock.
+ * 	[91/07/30  17:35:53  dbg]
+ * 
+ * Revision 2.4  91/05/14  17:57:11  mrt
+ * 	Correcting copyright
+ * 
+ * Revision 2.3  91/02/14  14:20:14  mrt
+ * 	Changed to new Mach copyright
+ * 	[91/02/13  12:20:00  mrt]
+ * 
+ * Revision 2.2  90/11/05  14:37:23  rpd
+ * 	Created.
+ * 	[90/11/01            rwd]
+ * 
+ *
+ */
+
+#ifndef _MACHINE_CTHREADS_H_
+#define _MACHINE_CTHREADS_H_
+
+typedef volatile int spin_lock_t;
+#define SPIN_LOCK_INITIALIZER	0
+#define spin_lock_init(s)	(*(s) = 0)
+#define spin_lock_locked(s)	(*(s) != 0)
+
+#ifdef	__GNUC__
+
+#define	spin_unlock(p) \
+	({  register int _u__ ; \
+	    asm volatile("xorl %0, %0; \n\
+			  xchgl %0, %1" \
+			: "=&r" (_u__), "=m" (*(p)) ); \
+	    0; })
+
+#define	spin_try_lock(p)\
+	({  boolean_t _r__; \
+	    asm volatile("movl $1, %0; \n\
+			  xchgl %0, %1" \
+			: "=&r" (_r__), "=m" (*(p)) ); \
+	    !_r__; })
+
+#define	cthread_sp() \
+	({  int	_sp__; \
+	    asm("movl %%esp, %0" \
+	      :	"=g" (_sp__) ); \
+	    _sp__; })
+
+#endif	/* __GNUC__ */
+
+#endif _MACHINE_CTHREADS_H_