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.. title:: clang-tidy - modernize-use-std-numbers
modernize-use-std-numbers
=========================
Finds constants and function calls to math functions that can be replaced
with C++20's mathematical constants from the ``numbers`` header and offers
fix-it hints.
Does not match the use of variables with that value, and instead,
offers a replacement for the definition of those variables.
Function calls that match the pattern of how the constant is calculated are
matched and replaced with the ``std::numbers`` constant.
The use of macros gets replaced with the corresponding ``std::numbers``
constant, instead of changing the macro definition.
The following list of constants from the ``numbers`` header are supported:
* ``e``
* ``log2e``
* ``log10e``
* ``pi``
* ``inv_pi``
* ``inv_sqrtpi``
* ``ln2``
* ``ln10``
* ``sqrt2``
* ``sqrt3``
* ``inv_sqrt3``
* ``egamma``
* ``phi``
The list currently includes all constants as of C++20.
The replacements use the type of the matched constant and can remove explicit
casts, i.e., switching between ``std::numbers::e``,
``std::numbers::e_v<float>`` and ``std::numbers::e_v<long double>`` where
appropriate.
.. code-block:: c++
double sqrt(double);
double log2(double);
void sink(auto&&) {}
void floatSink(float);
#define MY_PI 3.1415926
void foo() {
const double Pi = 3.141592653589; // const double Pi = std::numbers::pi
const auto Use = Pi / 2; // no match for Pi
static constexpr double Euler = 2.7182818; // static constexpr double Euler = std::numbers::e;
log2(exp(1)); // std::numbers::log2e;
log2(Euler); // std::numbers::log2e;
1 / sqrt(MY_PI); // std::numbers::inv_sqrtpi;
sink(MY_PI); // sink(std::numbers::pi);
floatSink(MY_PI); // floatSink(std::numbers::pi);
floatSink(static_cast<float>(MY_PI)); // floatSink(std::numbers::pi_v<float>);
}
Options
-------
.. option:: DiffThreshold
A floating point value that sets the detection threshold for when literals
match a constant. A literal matches a constant if
``abs(literal - constant) < DiffThreshold`` evaluates to ``true``. Default
is `0.001`.
.. option:: IncludeStyle
A string specifying which include-style is used, `llvm` or `google`. Default
is `llvm`.
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