std::signbit - cppreference.com (original) (raw)
| Defined in header | ||
|---|---|---|
| (1) | ||
| bool signbit( float num ); bool signbit( double num ); bool signbit( long double num ); | (since C++11) (until C++23) | |
| constexpr bool signbit( /*floating-point-type*/ num ); | (since C++23) | |
| SIMD overload (since C++26) | ||
| Defined in header | ||
| template< /*math-floating-point*/ V > constexpr typename /*deduced-simd-t*/<V>::mask_type signbit ( const V& v_num ); | (S) | (since C++26) |
| Additional overloads | ||
| Defined in header | ||
| template< class Integer > bool signbit( Integer num ); | (A) | (since C++11) (constexpr since C++23) |
- Determines if the given floating point number num is negative. The library provides overloads for all cv-unqualified floating-point types as the type of the parameter num.(since C++23)
A) Additional overloads are provided for all integer types, which are treated as double.
[edit] Parameters
| num | - | floating-point or integer value |
|---|---|---|
| v_num | - | a data-parallel object of std::basic_simd specialization where its element type is a floating-point type |
[edit] Return value
- true if num is negative, false otherwise.
S) A data-parallel mask object where the ith element equals true if v_num[i] is negative or false otherwise for all i in the range [0, v_num.size()).
[edit] Notes
This function detects the sign bit of zeroes, infinities, and NaNs. Along with std::copysign, std::signbit is one of the only two portable ways to examine the sign of a NaN.
The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::signbit(num) has the same effect as std::signbit(static_cast<double>(num)).
[edit] Example
#include #include int main() { std::cout << std::boolalpha << "signbit(+0.0) = " << std::signbit(+0.0) << '\n' << "signbit(-0.0) = " << std::signbit(-0.0) << '\n' << "signbit(+nan) = " << std::signbit(+NAN) << '\n' << "signbit(-nan) = " << std::signbit(-NAN) << '\n' << "signbit(+inf) = " << std::signbit(+INFINITY) << '\n' << "signbit(-inf) = " << std::signbit(-INFINITY) << '\n'; }
Output:
signbit(+0.0) = false signbit(-0.0) = true signbit(+nan) = false signbit(-nan) = true signbit(+inf) = false signbit(-inf) = true