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.

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

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.

IncludeStyle

A string specifying which include-style is used, llvm or google. Default is llvm.