std::signbit
From cppreference.com
| Defined in header <cmath>
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| (1) | ||
bool signbit( float num ); bool signbit( double num ); |
(since C++11) (until C++23) |
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| constexpr bool signbit( /*floating-point-type*/ num ); |
(since C++23) | |
| SIMD overload (since C++26) |
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| Defined in header <simd>
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| template< /*math-floating-point*/ V > constexpr typename /*deduced-simd-t*/<V>::mask_type |
(S) | (since C++26) |
| Defined in header <cmath>
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| template< class Integer > bool signbit( Integer num ); |
(A) | (since C++11) (constexpr since C++23) |
1) 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)
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S) The SIMD overload performs an element-wise
std::signbit on v_num.
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(since C++26) |
A) Additional overloads are provided for all integer types, which are treated as double.
Contents |
[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
1) 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
Run this code
#include <cmath> #include <iostream> 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
[edit] See also
| (C++11)(C++11) |
absolute value of a floating point value (|x|) (function) |
| (C++11)(C++11)(C++11) |
copies the sign of a floating point value (function) |
| C documentation for signbit
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