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Teuchos_SetScientific.hpp
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41 
42 #ifndef TEUCHOS_SET_SCIENTIFIC_HPP
43 #define TEUCHOS_SET_SCIENTIFIC_HPP
44 
45 #include <Teuchos_as.hpp>
46 #include <Teuchos_ScalarTraits.hpp>
47 #include <string>
48 #include <ios>
49 
50 namespace Teuchos {
51 
72 template<typename Scalar, const bool isFloatingPoint = ! Teuchos::ScalarTraits<Scalar>::isOrdinal>
74 
75 
76 // Partial specialization of SetScientific for floating-point types.
77 //
78 // This class currently requires that std::log10() take
79 // arguments of type Scalar. This may be relaxed in the future
80 // if Teuchos::ScalarTraits gets its own log10() method.
81 template<typename Scalar>
82 class SetScientific<Scalar, true> {
83  public:
84  typedef Scalar scalar_type;
85 
86  SetScientific(std::ostream& out, int prec = -1):
87  out_(out),
88  originalFlags_(out.flags()),
89  originalPrecision_(out.precision())
90  {
91  // Print floating-point values in scientific notation.
92  out << std::scientific;
93 
95 
96  // Set the number of (decimal) digits after the decimal
97  // point to print.
98  out.precision(static_cast<std::streamsize>(prec));
99  }
100 
101  static inline int getDefaultPrecision() {
103  typedef typename STS::magnitudeType magnitude_type;
105 
106  // We're writing decimal digits, so compute the number of
107  // digits we need to get reasonable accuracy when reading
108  // values back in.
109  //
110  // There is actually an algorithm, due to Guy Steele (yes,
111  // Java's Guy Steele) et al., for idempotent printing of
112  // finite-length floating-point values. We should actually
113  // implement that algorithm, but I don't have time for that
114  // now. Currently, I just print no more than (one decimal
115  // digit more than (the number of decimal digits justified
116  // by the precision of magnitude_type)).
117  //
118  // We need to use STM's log10() rather than (say) std::log10
119  // here, because STM::base() returns a magnitude_type, not
120  // one of C++'s standard integer types.
121  const magnitude_type numDecDigits = STM::t() * STM::log10 (STM::base());
122 
123  // Round and add one. The cast to int should not overflow
124  // unless STM::t() is _extremely_ large, so we don't need to
125  // check for that case here.
126  const magnitude_type one = STM::one();
127  const magnitude_type two = one + one;
128  // Cast from magnitude_type to int, since std::ostream's
129  // precision() method expects an int input.
130  const int prec = 1 +
131  Teuchos::as<int>(magnitude_type((two*numDecDigits + one) / two));
132  return prec;
133  }
134 
135  ~SetScientific () {
136  out_.flags (originalFlags_);
137  }
138 
139  private:
141  std::ostream& out_;
142 
144  std::ios_base::fmtflags originalFlags_;
145 
147  std::streamsize originalPrecision_;
148 };
149 
151 template<class Scalar>
152 class SetScientific<Scalar, false> {
153  public:
154  typedef Scalar scalar_type;
155  SetScientific(std::ostream&) {}
156  ~SetScientific() {}
157 };
158 
159 } // namespace Teuchos
160 
161 #endif // TEUCHOS_SET_SCIENTIFIC_HPP
Temporarily make an output stream use scientific notation with sufficient precision.
This structure defines some basic traits for a scalar field type.
Defines basic traits for the scalar field type.
Definition of Teuchos::as, for conversions between types.