lib cleanup

[SVN r15689]

doc/examples/linear_fib.c

@@ -0,0 +1,92 @@
+# /* 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.
+#  */
+#
+# /* Revised by Paul Mensonides (2002) */
+#
+# /* See http://www.boost.org for most recent version. */
+#
+# /* This example shows how BOOST_PP_WHILE() can be used for implementing macros. */
+#
+# include <stdio.h>
+#
+# include <boost/preprocessor/arithmetic/add.hpp>
+# include <boost/preprocessor/arithmetic/sub.hpp>
+# include <boost/preprocessor/comparison/less_equal.hpp>
+# include <boost/preprocessor/control/while.hpp>
+# include <boost/preprocessor/list/adt.hpp>
+# include <boost/preprocessor/tuple/elem.hpp>
+#
+# /* First consider the following C implementation of Fibonacci. */
+
+typedef struct linear_fib_state {
+   int a0, a1, n;
+} linear_fib_state;
+
+static int linear_fib_c(linear_fib_state p) {
+   return p.n;
+}
+
+static linear_fib_state linear_fib_f(linear_fib_state p) {
+   linear_fib_state r = { p.a1, p.a0 + p.a1, p.n - 1 };
+   return r;
+}
+
+static int linear_fib(int n) {
+   linear_fib_state p = { 0, 1, n };
+   while (linear_fib_c(p)) {
+      p = linear_fib_f(p);
+   }
+   return p.a0;
+}
+
+# /* Then consider the following preprocessor implementation of Fibonacci. */
+#
+# define LINEAR_FIB(n) LINEAR_FIB_D(1, n)
+# /* Since the macro is implemented using BOOST_PP_WHILE, the actual
+#  * implementation takes a depth as a parameters so that it can be called
+#  * inside a BOOST_PP_WHILE.  The above easy-to-use version simply uses 1
+#  * as the depth and cannot be called inside a BOOST_PP_WHILE.
+#  */
+#
+# define LINEAR_FIB_D(d, n) \
+   BOOST_PP_TUPLE_ELEM(3, 0, BOOST_PP_WHILE_ ## d(LINEAR_FIB_C, LINEAR_FIB_F, (0, 1, n)))
+# /*                   ^^^^                 ^^^^^           ^^            ^^   ^^^^^^^
+#  *                    #1                   #2             #3            #3     #4
+#  *
+#  * 1) The state is a 3-element tuple.  After the iteration is finished, the first
+#  *    element of the tuple is the result.
+#  *
+#  * 2) The WHILE primitive is "invoked" directly.  BOOST_PP_WHILE(D, ...)
+#  *    can't be used because it would not be expanded by the preprocessor.
+#  *
+#  * 3) ???_C is the condition and ???_F is the iteration macro.
+#  */
+#
+# define LINEAR_FIB_C(d, p) \
+   /* p.n */ BOOST_PP_TUPLE_ELEM(3, 2, p) \
+   /**/
+#
+# define LINEAR_FIB_F(d, p) \
+   ( \
+      /* p.a1 */ BOOST_PP_TUPLE_ELEM(3, 1, p), \
+      /* p.a0 + p.a1 */ BOOST_PP_ADD_D(d, BOOST_PP_TUPLE_ELEM(3, 0, p), BOOST_PP_TUPLE_ELEM(3, 1, p)), \
+                        /*          ^^ ^ \
+                         * BOOST_PP_ADD() uses BOOST_PP_WHILE().  Therefore we \
+                         * pass the recursion depth explicitly to BOOST_PP_ADD_D(). \
+                         */ \
+      /* p.n - 1 */ BOOST_PP_DEC(BOOST_PP_TUPLE_ELEM(3, 2, p)) \
+   ) \
+   /**/
+
+int main() {
+   printf("linear_fib(10) = %d\n", linear_fib(10));
+   printf("LINEAR_FIB(10) = %d\n", LINEAR_FIB(10));
+   return 0;
+}