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diff --git a/i386/util/i16/i16.h b/i386/util/i16/i16.h
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+++ b/i386/util/i16/i16.h
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+/* 
+ * Copyright (c) 1995-1994 The University of Utah and
+ * the Computer Systems Laboratory at the University of Utah (CSL).
+ * All rights reserved.
+ *
+ * Permission to use, copy, modify and distribute this software is hereby
+ * granted provided that (1) source code retains these copyright, permission,
+ * and disclaimer notices, and (2) redistributions including binaries
+ * reproduce the notices in supporting documentation, and (3) all advertising
+ * materials mentioning features or use of this software display the following
+ * acknowledgement: ``This product includes software developed by the
+ * Computer Systems Laboratory at the University of Utah.''
+ *
+ * THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS
+ * IS" CONDITION.  THE UNIVERSITY OF UTAH AND CSL DISCLAIM ANY LIABILITY OF
+ * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
+ *
+ * CSL requests users of this software to return to csl-dist@cs.utah.edu any
+ * improvements that they make and grant CSL redistribution rights.
+ *
+ *      Author: Bryan Ford, University of Utah CSL
+ */
+#ifndef _I386_I16_
+#define _I386_I16_
+
+#include <mach/machine/code16.h>
+
+#include "gdt.h"
+
+
+/* Macros to switch between 16-bit and 32-bit code
+   in the middle of a C function.
+   Be careful with these!  */
+#define i16_switch_to_32bit() asm volatile("
+		ljmp	%0,$1f
+		.code32
+	1:
+	" : : "i" (KERNEL_CS));
+#define switch_to_16bit() asm volatile("
+		ljmp	%0,$1f
+		.code16
+	1:
+	" : : "i" (KERNEL_16_CS));
+
+
+/* From within one type of code, execute 'stmt' in the other.
+   These are safer and harder to screw up with than the above macros.  */
+#define i16_do_32bit(stmt) \
+	({	i16_switch_to_32bit(); \
+		{ stmt; } \
+		switch_to_16bit(); })
+#define do_16bit(stmt) \
+	({	switch_to_16bit(); \
+		{ stmt; } \
+		i16_switch_to_32bit(); })
+
+
+#endif _I386_I16_