Added Duff's Device example

[SVN r12949]

doc/reference/repeat.htm

@@ -42,6 +42,7 @@
 
 <h3>Example</h3>
 <ul>
+  <li><a href="../../example/duffs_device.c">duffs_device.c</a></li>
   <li><a href="../../example/repeat_2d.c">repeat_2d.c</a></li>
 </ul>
 

example/duffs_device.c

@@ -0,0 +1,61 @@
+/* Copyright (C) 2002
+ * Housemarque Oy
+ * http://www.housemarque.com
+ *
+ * Permission to copy, use, modify, sell and distribute this software is
+ * granted provided this copyright notice appears in all copies. This
+ * software is provided "as is" without express or implied warranty, and
+ * with no claim as to its suitability for any purpose.
+ *
+ * See http://www.boost.org for most recent version.
+ */
+
+/* This example uses the preprocessor library to implement a generalized
+ * macro for implementing a Duff's Device.
+ *
+ * This example was inspired by an original generalized macro for
+ * implementing Duff's Device written by Joerg Walter.
+ */
+
+#include <boost/preprocessor/repeat.hpp>
+#include <boost/preprocessor/tuple/elem.hpp>
+#include <assert.h>
+
+/* Expands to a Duff's Device. */
+#define DUFFS_DEVICE(UNROLLING_FACTOR,COUNTER_TYPE,N,STATEMENT)\
+  do\
+  {\
+    COUNTER_TYPE\
+      duffs_device_initial_cnt = (N),\
+      duffs_device_running_cnt = (duffs_device_initial_cnt + (UNROLLING_FACTOR-1))/UNROLLING_FACTOR;\
+    switch (duffs_device_initial_cnt % UNROLLING_FACTOR)\
+    {\
+      do\
+      {\
+        BOOST_PP_REPEAT(UNROLLING_FACTOR,DUFFS_DEVICE_C,(UNROLLING_FACTOR,{STATEMENT}))\
+      } while (--duffs_device_running_cnt);\
+    }\
+  } while (0)
+
+#define DUFFS_DEVICE_C(I,UNROLLING_FACTOR_STATEMENT)\
+  case (I?BOOST_PP_TUPLE_ELEM(2,0,UNROLLING_FACTOR_STATEMENT)-I:0): BOOST_PP_TUPLE_ELEM(2,1,UNROLLING_FACTOR_STATEMENT);
+
+
+#ifndef UNROLLING_FACTOR
+#define UNROLLING_FACTOR 16
+#endif
+
+#ifndef N
+#define N 1000
+#endif
+
+int main(void)
+{
+  int i=0;
+
+  DUFFS_DEVICE(UNROLLING_FACTOR, int, N, ++i;);
+
+  assert(i == N);
+
+  return 0;
+}

include/boost/preprocessor/repeat.hpp

@@ -28,6 +28,7 @@ BOOST_PP_REPEAT_3RD() macros.</p>
 
 <h3>Example</h3>
 <ul>
+  <li><a href="../../example/duffs_device.c">duffs_device.c</a></li>
   <li><a href="../../example/repeat_2d.c">repeat_2d.c</a></li>
 </ul>