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BOOST_STATIC_ASSERT BOOST_STATIC_CONST boost::enable_if/disable_if Changed many traits class usages from boost:: to std::.
93 lines
5.3 KiB
Plaintext
93 lines
5.3 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:cpp_bin_float cpp_bin_float]
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`#include <boost/multiprecision/cpp_bin_float.hpp>`
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namespace boost{ namespace multiprecision{
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enum digit_base_type
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{
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digit_base_2 = 2,
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digit_base_10 = 10
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};
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template <unsigned Digits, digit_base_type base = digit_base_10, class Allocator = void, class Exponent = int, ExponentMin = 0, ExponentMax = 0>
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class cpp_bin_float;
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typedef number<cpp_bin_float<50> > cpp_bin_float_50;
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typedef number<cpp_bin_float<100> > cpp_bin_float_100;
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typedef number<backends::cpp_bin_float<24, backends::digit_base_2, void, std::int16_t, -126, 127>, et_off> cpp_bin_float_single;
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typedef number<backends::cpp_bin_float<53, backends::digit_base_2, void, std::int16_t, -1022, 1023>, et_off> cpp_bin_float_double;
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typedef number<backends::cpp_bin_float<64, backends::digit_base_2, void, std::int16_t, -16382, 16383>, et_off> cpp_bin_float_double_extended;
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typedef number<backends::cpp_bin_float<113, backends::digit_base_2, void, std::int16_t, -16382, 16383>, et_off> cpp_bin_float_quad;
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typedef number<backends::cpp_bin_float<237, backends::digit_base_2, void, std::int32_t, -262142, 262143>, et_off> cpp_bin_float_oct;
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}} // namespaces
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The `cpp_bin_float` back-end is used in conjunction with `number`: It acts as an entirely C++ (header only and dependency free)
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floating-point 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 `cpp_bin_float` can be used at fixed precision by specifying a non-zero `Digits` template parameter.
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The typedefs `cpp_bin_float_50` and `cpp_bin_float_100` provide arithmetic types at 50 and 100 decimal digits precision
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respectively.
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Optionally, you can specify whether the precision is specified in decimal digits or binary bits - for example
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to declare a `cpp_bin_float` with exactly the same precision as `double` one would use
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`number<cpp_bin_float<53, digit_base_2> >`. The typedefs `cpp_bin_float_single`, `cpp_bin_float_double`,
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`cpp_bin_float_quad`, `cpp_bin_float_oct` and `cpp_bin_float_double_extended` provide
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software analogues of the IEEE single, double, quad and octuple float data types, plus the Intel-extended-double type respectively.
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Note that while these types are functionally equivalent to the native IEEE types, but they do not have the same size
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or bit-layout as true IEEE compatible types.
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Normally `cpp_bin_float` allocates no memory: all of the space required for its digits are allocated
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directly within the class. As a result care should be taken not to use the class with too high a digit count
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as stack space requirements can grow out of control. If that represents a problem then providing an allocator
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as a template parameter causes `cpp_bin_float` to dynamically allocate the memory it needs: this
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significantly reduces the size of `cpp_bin_float` and increases the viable upper limit on the number of digits
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at the expense of performance. However, please bear in mind that arithmetic operations rapidly become ['very] expensive
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as the digit count grows: the current implementation really isn't optimized or designed for large digit counts.
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Note that since the actual type of the objects allocated
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is completely opaque, the suggestion would be to use an allocator with `void` `value_type`, for example:
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`number<cpp_bin_float<1000, digit_base_10, std::allocator<void> > >`.
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The final template parameters determine the type and range of the exponent: parameter `Exponent` can be
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any signed integer type, but note that `MinExponent` and `MaxExponent` can not go right up to the limits
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of the `Exponent` type as there has to be a little extra headroom for internal calculations. You will
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get a compile time error if this is the case. In addition if MinExponent or MaxExponent are zero, then
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the library will choose suitable values that are as large as possible given the constraints of the type
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and need for extra headroom for internal calculations.
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There is full standard library and `numeric_limits` support available for this type.
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Things you should know when using this type:
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* Default constructed `cpp_bin_float`s have a value of zero.
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* The radix of this type is 2, even when the precision is specified as decimal digits.
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* The type supports both infinities and NaNs. An infinity is generated whenever the result would overflow,
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and a NaN is generated for any mathematically undefined operation.
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* There is a `std::numeric_limits` specialisation for this type.
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* Any `number` instantiated on this type, is convertible to any other `number` instantiated on this type -
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for example you can convert from `number<cpp_bin_float<50> >` to `number<cpp_bin_float<SomeOtherValue> >`.
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Narrowing conversions round to nearest and are `explicit`.
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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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* All arithmetic operations are correctly rounded to nearest. String conversions and the `sqrt` function
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are also correctly rounded, but transcendental functions (sin, cos, pow, exp etc) are not.
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[h5 cpp_bin_float example:]
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[cpp_bin_float_eg]
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[endsect]
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