ceph/src/boost/libs/preprocessor/doc/examples/duffs_device.c

   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
  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 }