+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (c) 2009 Mathieu Desnoyers
+ */
+
+/* 16 CPUs max (byte has 8 bits, divided in two) */
+
+#ifndef CONFIG_BITS_PER_BYTE
+#define BITS_PER_BYTE 8
+#else
+#define BITS_PER_BYTE CONFIG_BITS_PER_BYTE
+#endif
+
+#define HBPB (BITS_PER_BYTE / 2) /* 4 */
+#define HMASK ((1 << HBPB) - 1) /* 0x0F */
+
+/* for byte type */
+#define LOW_HALF(val) ((val) & HMASK)
+#define LOW_HALF_INC 1
+
+#define HIGH_HALF(val) ((val) & (HMASK << HBPB))
+#define HIGH_HALF_INC (1 << HBPB)
+
+byte lock = 0;
+byte refcount = 0;
+
+inline spin_lock(lock, ticket)
+{
+ atomic {
+ ticket = HIGH_HALF(lock) >> HBPB;
+ lock = lock + HIGH_HALF_INC; /* overflow expected */
+ }
+
+ do
+ :: 1 ->
+ if
+ :: (LOW_HALF(lock) == ticket) ->
+ break;
+ :: else ->
+ skip;
+ fi;
+ od;
+}
+
+inline spin_unlock(lock)
+{
+ lock = HIGH_HALF(lock) | LOW_HALF(lock + LOW_HALF_INC);
+}
+
+proctype proc_X()
+{
+ byte ticket;
+
+ do
+ :: 1->
+ spin_lock(lock, ticket);
+ refcount = refcount + 1;
+ refcount = refcount - 1;
+ spin_unlock(lock);
+ od;
+}
+
+init
+{
+ run proc_X();
+ run proc_X();
+ run proc_X();
+ run proc_X();
+ run proc_X();
+}