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LSSTDataManagementBasePackage
SafeSum.h
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1 // -*- LSST-C++ -*-
2 /*
3  * Developed for the LSST Data Management System.
4  * This product includes software developed by the LSST Project
5  * (https://www.lsst.org).
6  * See the COPYRIGHT file at the top-level directory of this distribution
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22 #ifndef LSST_AFW_MATH_POLYNOMIALS_SafeSum_h_INCLUDED
23 #define LSST_AFW_MATH_POLYNOMIALS_SafeSum_h_INCLUDED
24 
25 #include <cmath>
26 
27 namespace lsst { namespace geom { namespace polynomials {
28 
32 enum class SumMode {
34  FAST,
36  SAFE
37 };
38 
61 template <typename T>
62 class SafeSum {
63 public:
64 
65  explicit SafeSum(T initial=static_cast<T>(0)) noexcept :
66  _sum(initial),
67  _correction(static_cast<T>(0))
68  {}
69 
70  SafeSum & operator=(T value) noexcept {
71  _sum = value;
72  _correction = static_cast<T>(0);
73  return *this;
74  }
75 
76  SafeSum & operator+=(T value) noexcept {
77  T t = _sum + value;
78  // update _correction to account for lost low-order bits of the
79  // greater of _sum and value
80  if (std::abs(_sum) >= std::abs(value)) {
81  _correction += (_sum - t) + value;
82  } else {
83  _correction += (value - t) + _sum;
84  }
85  _sum = t;
86  return *this;
87  }
88 
89  SafeSum & operator-=(T value) noexcept {
90  return operator+=(-value);
91  }
92 
93  explicit operator T() const noexcept {
94  return _sum + _correction;
95  }
96 
97 private:
98  T _sum;
99  T _correction;
100 };
101 
102 }}} // namespace lsst::geom::polynomials
103 
104 #endif // !LSST_AFW_MATH_POLYNOMIALS_SafeSum_h_INCLUDED
Angle abs(Angle const &a)
Definition: Angle.h:106
Summation using regular floating-point addition.
Extent< double, N > & operator+=(Extent< double, N > &lhs, Extent< int, N > const &rhs) noexcept
Definition: Extent.h:470
A numerically stable summation algorithm for floating-point numbers.
Definition: SafeSum.h:62
SafeSum(T initial=static_cast< T >(0)) noexcept
Definition: SafeSum.h:65
SafeSum & operator=(T value) noexcept
Definition: SafeSum.h:70
SumMode
Enum used to control how to sum polynomial terms.
Definition: SafeSum.h:32
A base class for image defects.
SafeSum & operator-=(T value) noexcept
Definition: SafeSum.h:89
SafeSum & operator+=(T value) noexcept
Definition: SafeSum.h:76
Compensated summation using SafeSum. Involves ~4x as many floating point operations.