ceph/src/boost/libs/math/include/boost/math/special_functions/sqrt1pm1.hpp

   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
  21 namespace boost{ namespace math{
  22
  23 template <class T, class Policy>
  24 inline 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
  34 template <class T>
  35 inline 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
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  48