1 # /* Copyright (C) 2002
2 # * Housemarque Oy
3 # * http://www.housemarque.com
4 # *
5 # * Distributed under the Boost Software License, Version 1.0. (See
6 # * accompanying file LICENSE_1_0.txt or copy at
7 # * http://www.boost.org/LICENSE_1_0.txt)
8 # */
9 #
10 # /* Revised by Paul Mensonides (2002) */
11 #
12 # /* See http://www.boost.org for most recent version. */
13 #
14 # /* This example uses the preprocessor library to implement a generalized
15 # * macro for implementing Duff's Device.
16 # *
17 # * This example was inspired by an original generalized macro for
18 # * for implementing Duff's Device written by Joerg Walter.
19 # */
20 #
21 # include <assert.h>
22 #
23 # include <boost/preprocessor/repetition/repeat.hpp>
24 # include <boost/preprocessor/tuple/elem.hpp>
25 #
26 # /* Expands to a Duff's Device. */
27 # define DUFFS_DEVICE(UNROLLING_FACTOR, COUNTER_TYPE, N, STATEMENT) \
28 do { \
29 COUNTER_TYPE duffs_device_initial_cnt = (N); \
30 if (duffs_device_initial_cnt > 0) { \
31 COUNTER_TYPE duffs_device_running_cnt = (duffs_device_initial_cnt + (UNROLLING_FACTOR - 1)) / UNROLLING_FACTOR; \
32 switch (duffs_device_initial_cnt % UNROLLING_FACTOR) { \
33 do { \
34 BOOST_PP_REPEAT(UNROLLING_FACTOR, DUFFS_DEVICE_C, (UNROLLING_FACTOR, { STATEMENT })) \
35 } while (--duffs_device_running_cnt); \
36 } \
37 } \
38 } while (0) \
39 /**/
40 #
41 # define DUFFS_DEVICE_C(Z, I, UNROLLING_FACTOR_STATEMENT) \
42 case (I ? BOOST_PP_TUPLE_ELEM(2, 0, UNROLLING_FACTOR_STATEMENT) - I : 0): \
43 BOOST_PP_TUPLE_ELEM(2, 1, UNROLLING_FACTOR_STATEMENT); \
44 /**/
45 #
46 # ifndef UNROLLING_FACTOR
47 # define UNROLLING_FACTOR 16
48 # endif
49 #
50 # ifndef N
51 # define N 1000
52 # endif
53
main(void)54 int main(void) {
55 int i = 0;
56 DUFFS_DEVICE(UNROLLING_FACTOR, int, 0, ++i;);
57 assert(i == 0);
58 DUFFS_DEVICE(UNROLLING_FACTOR, int, N, ++i;);
59 assert(i == N);
60 return 0;
61 }
62