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* Update Jamfile.v2 * Update introduction.qbk * Update tutorial.qbk * Update tutorial_cpp_int.qbk * Update tutorial_gmp_int.qbk * Update tutorial_tommath.qbk * Update integer_examples.cpp * Update tutorial_cpp_bin_float.qbk * Update tutorial_cpp_dec_float.qbk * Update tutorial_gmp_float.qbk * Update tutorial_mpfr_float.qbk * Update tutorial_float128.qbk * Update tutorial_float_builtin_ctor.qbk * Update big_seventh.cpp * Update tutorial_float_eg.qbk * Update floating_point_examples.cpp * Update mpfr_precision.cpp * Update gauss_laguerre_quadrature.cpp * Update tutorial_interval_mpfi.qbk * Update tutorial_cpp_complex.qbk * Update tutorial_mpc_complex.qbk * Update tutorial_float128_complex.qbk * Update tutorial_complex_adaptor.qbk * Update tutorial_rational.qbk * Update tutorial_tommath_rational.qbk * Update tutorial_logged_adaptor.qbk * Update tutorial_debug_adaptor.qbk * Update tutorial_visualizers.qbk * Update tutorial_fwd.qbk * Update tutorial_conversions.qbk * Update tutorial_random.qbk * Update random_snips.cpp * Update tutorial_constexpr.qbk * Update tutorial_import_export.qbk * Update cpp_int_import_export.cpp * Update tutorial_mixed_precision.qbk * Update tutorial_variable_precision.qbk * Update scoped_precision_example.cpp * Update tutorial_numeric_limits.qbk * Update tutorial_numeric_limits.qbk * Update numeric_limits_snips.cpp * Update numeric_limits_snips.cpp * Update tutorial_numeric_limits.qbk * Update numeric_limits_snips.cpp * Update numeric_limits_snips.cpp * Update tutorial_io.qbk * Update reference_number.qbk * Update reference_cpp_bin_float.qbk * Update reference_cpp_double_fp_backend.qbk * Update reference_internal_support.qbk * Update reference_backend_requirements.qbk * Update performance.qbk * Update performance_overhead.qbk * Update performance_real_world.qbk * Update performance_integer_real_world.qbk * Update performance_rational_real_world.qbk * Update reference_number.qbk * Update tutorial_numeric_limits.qbk * Update reference_backend_requirements.qbk
72 lines
3.3 KiB
Plaintext
72 lines
3.3 KiB
Plaintext
[/
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Copyright 2011 - 2020 John Maddock.
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Copyright 2013 - 2019 Paul A. Bristow.
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Copyright 2013 Christopher Kormanyos.
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt).
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]
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[section:gmp_float gmp_float]
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`#include <boost/multiprecision/gmp.hpp>`
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namespace boost{ namespace multiprecision{
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template <unsigned Digits10>
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class gmp_float;
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typedef number<gmp_float<50> > mpf_float_50;
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typedef number<gmp_float<100> > mpf_float_100;
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typedef number<gmp_float<500> > mpf_float_500;
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typedef number<gmp_float<1000> > mpf_float_1000;
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typedef number<gmp_float<0> > mpf_float;
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}} // namespaces
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The `gmp_float` back-end is used in conjunction with `number`: it acts as a thin wrapper around the [gmp] `mpf_t`
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to provide a real-number type that is a drop-in replacement for the native C++ floating-point types, but with
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much greater precision.
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Type `gmp_float` can be used at fixed precision by specifying a non-zero `Digits10` template parameter, or
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at variable precision by setting the template argument to zero. The typedefs mpf_float_50, mpf_float_100,
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mpf_float_500, mpf_float_1000 provide arithmetic types at 50, 100, 500 and 1000 decimal digits precision
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respectively. The typedef mpf_float provides a variable precision type whose precision can be controlled via the
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`number`s member functions.
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[note This type only provides standard library and `numeric_limits` support when the precision is fixed at compile time.]
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As well as the usual conversions from arithmetic and string types, instances of `number<mpf_float<N> >` are
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copy constructible and assignable from:
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* The [gmp] native types `mpf_t`, `mpz_t`, `mpq_t`.
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* The `number` wrappers around those types: `number<mpf_float<M> >`, `number<gmp_int>`, `number<gmp_rational>`.
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It's also possible to access the underlying `mpf_t` via the `data()` member function of `gmp_float`.
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Things you should know when using this type:
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* Default constructed `gmp_float`s have the value zero (this is the [gmp] library's default behavior).
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* No changes are made to the [gmp] library's global settings, so this type can be safely mixed with
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existing [gmp] code.
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* This backend supports rvalue-references and is move-aware, making instantiations of `number` on this backend move-aware.
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* It is not possible to round-trip objects of this type to and from a string and get back
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exactly the same value. This appears to be a limitation of [gmp].
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* Since the underlying [gmp] types have no notion of infinities or NaNs, care should be taken
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to avoid numeric overflow or division by zero. That latter will result in a std::overflow_error being thrown,
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while generating excessively large exponents may result in instability of the underlying [gmp]
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library (in testing, converting a number with an excessively large or small exponent
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to a string caused [gmp] to segfault).
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* This type can equally be used with [mpir] as the underlying implementation - indeed that is
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the recommended option on Win32.
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* Conversion from a string results in a `std::runtime_error` being thrown if the string can not be interpreted
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as a valid floating-point number.
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* Division by zero results in a `std::overflow_error` being thrown.
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[h5 [gmp] example:]
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[mpf_eg]
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[endsect]
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