af0d731b12
Implementing the Hermite polynomials which are part of C++17's mathematical special functions. The goal is to get early feedback which will make implementing the other functions easier. Integration of functions in chunks (e.g. `std::hermite` at first, then `std::laguerre`, etc.) might make sense as well (also see note on boost.math below). I started out from this abandoned merge request: https://reviews.llvm.org/D58876 . The C++23 standard defines them in-terms of `/* floating-point type */` arguments. I have not looked into that. Note, there is still an ongoing discussion on discourse whether importing boost.math is an option.
70 lines
2.8 KiB
ReStructuredText
70 lines
2.8 KiB
ReStructuredText
.. _implementation-defined-behavior:
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===============================
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Implementation-defined behavior
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===============================
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Contains the implementation details of the implementation-defined behavior in
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libc++. Implementation-defined is mandated to be documented by the Standard.
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.. note:
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This page is far from complete.
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Implementation-defined behavior
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===============================
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Updating the Time Zone Database
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-------------------------------
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The Standard allows implementations to automatically update the
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*remote time zone database*. Libc++ opts not to do that. Instead calling
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- ``std::chrono::remote_version()`` will update the version information of the
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*remote time zone database*,
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- ``std::chrono::reload_tzdb()``, if needed, will update the entire
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*remote time zone database*.
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This offers a way for users to update the *remote time zone database* and
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give them full control over the process.
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`[ostream.formatted.print]/3 <http://eel.is/c++draft/ostream.formatted.print#3>`_ A terminal capable of displaying Unicode
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--------------------------------------------------------------------------------------------------------------------------
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The Standard specifies that the manner in which a stream is determined to refer
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to a terminal capable of displaying Unicode is implementation-defined. This is
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used for ``std::print`` and similar functions taking an ``ostream&`` argument.
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Libc++ determines that a stream is Unicode-capable terminal by:
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* First it determines whether the stream's ``rdbuf()`` has an underlying
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``FILE*``. This is ``true`` in the following cases:
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* The stream is ``std::cout``, ``std::cerr``, or ``std::clog``.
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* A ``std::basic_filebuf<CharT, Traits>`` derived from ``std::filebuf``.
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* The way to determine whether this ``FILE*`` refers to a terminal capable of
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displaying Unicode is the same as specified for `void vprint_unicode(FILE*
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stream, string_view fmt, format_args args);
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<http://eel.is/c++draft/print.fun#7>`_. This function is used for other
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``std::print`` overloads that don't take an ``ostream&`` argument.
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`[sf.cmath] <https://wg21.link/sf.cmath>`_ Mathematical Special Functions: Large indices
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----------------------------------------------------------------------------------------
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Most functions within the Mathematical Special Functions section contain integral indices.
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The Standard specifies the result for larger indices as implementation-defined.
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Libc++ pursuits reasonable results by choosing the same formulas as for indices below that threshold.
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E.g.
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- ``std::hermite(unsigned n, T x)`` for ``n >= 128``
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Listed in the index of implementation-defined behavior
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======================================================
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The order of the entries matches the entries in the
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`draft of the Standard <http://eel.is/c++draft/impldefindex>`_.
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