# Extra Clang Tools 18.1.8 documentation

## 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.

    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.