Boost_1_39_0/libs/numeric/interval/examples/horner.cpp

   1 /* Boost example/horner.cpp
   2  * example of unprotecting rounding for a whole function computation
   3  *
   4  * Copyright 2002-2003 Guillaume Melquiond
   5  *
   6  * Distributed under the Boost Software License, Version 1.0.
   7  * (See accompanying file LICENSE_1_0.txt or
   8  * copy at http://www.boost.org/LICENSE_1_0.txt)
   9  */
  10
  11 #include <boost/numeric/interval.hpp>
  12 #include <iostream>
  13
  14 // I is an interval class, the polynom is a simple array
  15 template<class I>
  16 I horner(const I& x, const I p[], int n) {
  17
  18   // initialize and restore the rounding mode
  19   typename I::traits_type::rounding rnd;
  20
  21   // define the unprotected version of the interval type
  22   typedef typename boost::numeric::interval_lib::unprotect<I>::type R;
  23
  24   const R& a = x;
  25   R y = p[n - 1];
  26   for(int i = n - 2; i >= 0; i--) {
  27     y = y * a + (const R&)(p[i]);
  28   }
  29   return y;
  30
  31   // restore the rounding mode with the destruction of rnd
  32 }
  33
  34 template<class T, class Policies>
  35 std::ostream &operator<<(std::ostream &os,
  36                          const boost::numeric::interval<T, Policies> &x) {
  37   os << "[" << x.lower() << ", " << x.upper() << "]";
  38   return os;
  39 }
  40
  41 int main() {
  42   typedef boost::numeric::interval<double> I;
  43   I p[3] = { -1.0, 0, 1.0 };
  44   I x = 1.0;
  45   std::cout << horner(x, p, 3) << std::endl;
  46   return 0;
  47 }