mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2025-10-31 04:50:34 -04:00
108 lines
2.8 KiB
C++
108 lines
2.8 KiB
C++
// Copyright John Maddock 2007.
|
|
// Copyright Paul A. Bristow 2010
|
|
|
|
// Use, modification and distribution are subject to the
|
|
// Boost Software License, Version 1.0. (See accompanying file
|
|
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
|
|
|
|
// Note that this file contains quickbook mark-up as well as code
|
|
// and comments, don't change any of the special comment mark-ups!
|
|
|
|
#include <iostream>
|
|
using std::cout; using std::endl;
|
|
#include <cerrno> // for ::errno
|
|
|
|
//[policy_eg_4
|
|
|
|
/*`
|
|
Suppose we want `C::foo()` to behave in a C-compatible way and set
|
|
`::errno` on error rather than throwing any exceptions.
|
|
|
|
We'll begin by including the needed header for our function:
|
|
*/
|
|
|
|
#include <boost/math/special_functions.hpp>
|
|
//using boost::math::tgamma; // Not needed because using C::tgamma.
|
|
|
|
/*`
|
|
Open up the "C" namespace that we'll use for our functions, and
|
|
define the policy type we want: in this case a C-style one that sets
|
|
::errno and returns a standard value, rather than throwing exceptions.
|
|
|
|
Any policies we don't specify here will inherit the defaults.
|
|
*/
|
|
|
|
namespace C
|
|
{ // To hold our C-style policy.
|
|
//using namespace boost::math::policies; or explicitly:
|
|
using boost::math::policies::policy;
|
|
|
|
using boost::math::policies::domain_error;
|
|
using boost::math::policies::pole_error;
|
|
using boost::math::policies::overflow_error;
|
|
using boost::math::policies::evaluation_error;
|
|
using boost::math::policies::errno_on_error;
|
|
|
|
typedef policy<
|
|
domain_error<errno_on_error>,
|
|
pole_error<errno_on_error>,
|
|
overflow_error<errno_on_error>,
|
|
evaluation_error<errno_on_error>
|
|
> c_policy;
|
|
|
|
/*`
|
|
All we need do now is invoke the BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS
|
|
macro passing our policy type c_policy as the single argument:
|
|
*/
|
|
|
|
BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS(c_policy)
|
|
|
|
} // close namespace C
|
|
|
|
/*`
|
|
We now have a set of forwarding functions defined in namespace C
|
|
that all look something like this:
|
|
|
|
``
|
|
template <class RealType>
|
|
inline typename boost::math::tools::promote_args<RT>::type
|
|
tgamma(RT z)
|
|
{
|
|
return boost::math::tgamma(z, c_policy());
|
|
}
|
|
``
|
|
|
|
So that when we call `C::tgamma(z)`, we really end up calling
|
|
`boost::math::tgamma(z, C::c_policy())`:
|
|
*/
|
|
|
|
int main()
|
|
{
|
|
errno = 0;
|
|
cout << "Result of tgamma(30000) is: "
|
|
<< C::tgamma(30000) << endl; // Note using C::tgamma
|
|
cout << "errno = " << errno << endl; // errno = 34
|
|
cout << "Result of tgamma(-10) is: "
|
|
<< C::tgamma(-10) << endl;
|
|
cout << "errno = " << errno << endl; // errno = 33, overwriting previous value of 34.
|
|
}
|
|
|
|
/*`
|
|
|
|
Which outputs:
|
|
|
|
[pre
|
|
Result of C::tgamma(30000) is: 1.#INF
|
|
errno = 34
|
|
Result of C::tgamma(-10) is: 1.#QNAN
|
|
errno = 33
|
|
]
|
|
|
|
This mechanism is particularly useful when we want to define a project-wide policy,
|
|
and don't want to modify the Boost source,
|
|
or to set project wide build macros (possibly fragile and easy to forget).
|
|
|
|
*/
|
|
//] //[/policy_eg_4]
|
|
|