1// (C) Copyright John Maddock 2006.
2// Use, modification and distribution are subject to the
3// Boost Software License, Version 1.0. (See accompanying file
4// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
5
6#ifndef BOOST_MATH_SQRT1PM1
7#define BOOST_MATH_SQRT1PM1
8
9#ifdef _MSC_VER
10#pragma once
11#endif
12
13#include <boost/math/special_functions/math_fwd.hpp>
14#include <boost/math/special_functions/log1p.hpp>
15#include <boost/math/special_functions/expm1.hpp>
16
17//
18// This algorithm computes sqrt(1+x)-1 for small x:
19//
20
21namespace boost{ namespace math{
22
23template <class T, class Policy>
24inline typename tools::promote_args<T>::type sqrt1pm1(const T& val, const Policy& pol)
25{
26 typedef typename tools::promote_args<T>::type result_type;
27 BOOST_MATH_STD_USING
28
29 if(fabs(result_type(val)) > 0.75)
30 return sqrt(1 + result_type(val)) - 1;
31 return boost::math::expm1(boost::math::log1p(val, pol) / 2, pol);
32}
33
34template <class T>
35inline typename tools::promote_args<T>::type sqrt1pm1(const T& val)
36{
37 return sqrt1pm1(val, policies::policy<>());
38}
39
40} // namespace math
41} // namespace boost
42
43#endif // BOOST_MATH_SQRT1PM1
44
45
46
47
48
49

source code of include/boost/math/special_functions/sqrt1pm1.hpp