The BOOST_PP_SUB_D macro expands to the difference between its second and third arguments.  It reenters BOOST_PP_WHILE with maximum efficiency.

Usage

BOOST_PP_SUB_D(d, x, y)

Arguments

d
The next available BOOST_PP_WHILE iteration. 
x
The minuend of the operation.  Valid values range from 0 to BOOST_PP_LIMIT_MAG.
y
The subtrahend of the operation.  Valid values range from 0 to BOOST_PP_LIMIT_MAG.

Remarks

If the difference between x and y is less than 0, the result is saturated to 0.

See Also

Requirements

Header:  <boost/preprocessor/arithmetic/sub.hpp>

Sample Code

#include <boost/preprocessor/arithmetic/dec.hpp>
#include <boost/preprocessor/arithmetic/sub.hpp>
#include <boost/preprocessor/control/while.hpp>
#include <boost/preprocessor/tuple/elem.hpp>

#define PRED(d, data) BOOST_PP_TUPLE_ELEM(2, 0, data)

#define OP(d, data) \
   ( \
      BOOST_PP_DEC( \
         BOOST_PP_TUPLE_ELEM(2, 0, data) \
      ), \
      BOOST_PP_SUB_D( \
         d, \
         BOOST_PP_TUPLE_ELEM(2, 1, data), \
         2 \
      ) \
   ) \
   /**/

// decrement 'x' by 2 'n' times
#define STRIDE(x, n) BOOST_PP_TUPLE_ELEM(2, 1, BOOST_PP_WHILE(PRED, OP, (n, x)))

STRIDE(10, 2) // expands to 6
STRIDE(14, 6) // expands to 2

Copyright Housemarque Oy 2002
Copyright Paul Mensonides 2002

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at www.boost.org/LICENSE_1_0.txt)