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1.. title:: clang-tidy - modernize-use-std-numbers2 3modernize-use-std-numbers4=========================5 6Finds constants and function calls to math functions that can be replaced7with C++20's mathematical constants from the ``numbers`` header and offers8fix-it hints.9Does not match the use of variables with that value, and instead,10offers a replacement for the definition of those variables.11Function calls that match the pattern of how the constant is calculated are12matched and replaced with the ``std::numbers`` constant.13The use of macros gets replaced with the corresponding ``std::numbers``14constant, instead of changing the macro definition.15 16The following list of constants from the ``numbers`` header are supported:17 18* ``e``19* ``log2e``20* ``log10e``21* ``pi``22* ``inv_pi``23* ``inv_sqrtpi``24* ``ln2``25* ``ln10``26* ``sqrt2``27* ``sqrt3``28* ``inv_sqrt3``29* ``egamma``30* ``phi``31 32The list currently includes all constants as of C++20.33 34The replacements use the type of the matched constant and can remove explicit35casts, i.e., switching between ``std::numbers::e``,36``std::numbers::e_v<float>`` and ``std::numbers::e_v<long double>`` where37appropriate.38 39.. code-block:: c++40 41 double sqrt(double);42 double log2(double);43 void sink(auto&&) {}44 void floatSink(float);45 46 #define MY_PI 3.141592647 48 void foo() {49 const double Pi = 3.141592653589; // const double Pi = std::numbers::pi50 const auto Use = Pi / 2; // no match for Pi51 static constexpr double Euler = 2.7182818; // static constexpr double Euler = std::numbers::e;52 53 log2(exp(1)); // std::numbers::log2e;54 log2(Euler); // std::numbers::log2e;55 1 / sqrt(MY_PI); // std::numbers::inv_sqrtpi;56 sink(MY_PI); // sink(std::numbers::pi);57 floatSink(MY_PI); // floatSink(std::numbers::pi);58 floatSink(static_cast<float>(MY_PI)); // floatSink(std::numbers::pi_v<float>);59 }60 61Options62-------63 64.. option:: DiffThreshold65 66 A floating point value that sets the detection threshold for when literals67 match a constant. A literal matches a constant if68 ``abs(literal - constant) < DiffThreshold`` evaluates to ``true``. Default69 is `0.001`.70 71.. option:: IncludeStyle72 73 A string specifying which include-style is used, `llvm` or `google`. Default74 is `llvm`.75