std::signbit
Defined in header <cmath> | ||
|---|---|---|
bool signbit( float num ); bool signbit( double num ); bool signbit( long double num ); | (1) |
(since C++11) (until C++23) |
constexpr bool signbit( /*floating-point-type*/ num ); | (since C++23) | |
| SIMD overload (since C++26) | ||
Defined in header <simd> | ||
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 <cmath> | ||
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)
S) The SIMD overload performs an element-wise std::signbit on v_num. (See math-floating-point and deduced-simd-t for their definitions.) | (since C++26) |
A) Additional overloads are provided for all integer types, which are treated as double.
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 |
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()).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)).
Example
#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
See also
|
(C++11)(C++11) | absolute value of a floating point value (\(\small{|x|}\)|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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