Teuchos - Trilinos Tools Package Version of the Day
Teuchos_MatrixMarket_SetScientific.hpp
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00041 
00042 #ifndef __Teuchos_MatrixMarket_SetScientific_hpp
00043 #define __Teuchos_MatrixMarket_SetScientific_hpp
00044 
00045 #include <Teuchos_as.hpp>
00046 #include <Teuchos_ScalarTraits.hpp>
00047 #include <string>
00048 
00049 
00050 namespace Teuchos {
00051   namespace MatrixMarket {
00052     namespace details {
00077       template<class Scalar>
00078       class SetScientific {
00079       public:
00081         typedef Scalar scalar_type;
00082 
00087         SetScientific (std::ostream& out) :
00088           out_ (out), originalFlags_ (out.flags())
00089         {
00090           typedef Teuchos::ScalarTraits<scalar_type> STS;
00091           typedef typename STS::magnitudeType magnitude_type;
00092           typedef Teuchos::ScalarTraits<magnitude_type> STM;
00093 
00094           // Print floating-point values in scientific notation.
00095           out << std::scientific;
00096 
00097           // We're writing decimal digits, so compute the number of
00098           // digits we need to get reasonable accuracy when reading
00099           // values back in.
00100           //
00101           // There is actually an algorithm, due to Guy Steele (yes,
00102           // Java's Guy Steele) et al., for idempotent printing of
00103           // finite-length floating-point values.  We should actually
00104           // implement that algorithm, but I don't have time for that
00105           // now.  Currently, I just print no more than (one decimal
00106           // digit more than (the number of decimal digits justified
00107           // by the precision of magnitude_type)).
00108           //
00109           // We need to use STM's log10() rather than (say) std::log10
00110           // here, because STM::base() returns a magnitude_type, not
00111           // one of C++'s standard integer types.
00112           const magnitude_type numDecDigits = STM::t() * STM::log10 (STM::base());
00113 
00114           // Round and add one.  The cast to int should not overflow
00115           // unless STM::t() is _extremely_ large, so we don't need to
00116           // check for that case here.
00117           const magnitude_type one = STM::one();
00118           const magnitude_type two = one + one;
00119           // Cast from magnitude_type to int, since std::ostream's
00120           // precision() method expects an int input.
00121           const int prec = 1 + Teuchos::as<int> ((two*numDecDigits + one) / two);
00122 
00123           // Set the number of (decimal) digits after the decimal
00124           // point to print.
00125           out.precision (prec);
00126         }
00127 
00133         ~SetScientific () {
00134           out_.flags (originalFlags_);
00135         }
00136 
00137       private:
00139         std::ostream& out_;
00140 
00142         std::ios_base::fmtflags originalFlags_;
00143       };
00144 
00145     } // namespace details
00146   } // namespace MatrixMarket
00147 } // namespace Teuchos
00148 
00149 #endif // __Teuchos_MatrixMarket_SetScientific_hpp
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