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Defined in header <cmath> | ||
| (1) | ||
float frexp(float num,int* exp); double frexp(double num,int* exp); | (until C++23) | |
constexpr/* floating-point-type */ frexp(/* floating-point-type */ num,int* exp); | (since C++23) | |
float frexpf(float num,int* exp); | (2) | (since C++11) (constexpr since C++23) |
longdouble frexpl(longdouble num,int* exp); | (3) | (since C++11) (constexpr since C++23) |
Additional overloads(since C++11) | ||
Defined in header <cmath> | ||
template<class Integer> double frexp( Integer num,int* exp); | (A) | (constexpr since C++23) |
std::frexp for all cv-unqualified floating-point types as the type of the parameternum.(since C++23)A) Additional overloads are provided for all integer types, which are treated asdouble. | (since C++11) |
Contents |
| num | - | floating-point or integer value |
| exp | - | pointer to integer value to store the exponent to |
Ifnum is zero, returns zero and stores zero in*exp.
Otherwise (ifnum is not zero), if no errors occur, returns the valuex in the range(-1, -0.5], [0.5, 1) and stores an integer value in*exp such thatx×2(*exp)
== num.
If the value to be stored in*exp is outside the range ofint, the behavior is unspecified.
This function is not subject to any errors specified inmath_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
On a binary system (whereFLT_RADIX is2),std::frexp may be implemented as
{*exp=(value==0)?0:(int)(1+std::logb(value));returnstd::scalbn(value,-(*exp));}
The functionstd::frexp, together with its dual,std::ldexp, can be used to manipulate the representation of a floating-point number without direct bit manipulations.
The additional overloads are not required to be provided exactly as(A). They only need to be sufficient to ensure that for their argumentnum of integer type,std::frexp(num, exp) has the same effect asstd::frexp(static_cast<double>(num), exp).
Compares different floating-point decomposition functions:
#include <cmath>#include <iostream>#include <limits> int main(){double f=123.45;std::cout<<"Given the number "<< f<<" or "<<std::hexfloat<< f<<std::defaultfloat<<" in hex,\n"; double f3;double f2=std::modf(f,&f3);std::cout<<"modf() makes "<< f3<<" + "<< f2<<'\n'; int i; f2= std::frexp(f,&i);std::cout<<"frexp() makes "<< f2<<" * 2^"<< i<<'\n'; i=std::ilogb(f);std::cout<<"logb()/ilogb() make "<< f/std::scalbn(1.0, i)<<" * "<<std::numeric_limits<double>::radix<<"^"<<std::ilogb(f)<<'\n';}
Possible output:
Given the number 123.45 or 0x1.edccccccccccdp+6 in hex,modf() makes 123 + 0.45frexp() makes 0.964453 * 2^7logb()/ilogb() make 1.92891 * 2^6
(C++11)(C++11) | multiplies a number by2 raised to an integral power (function)[edit] |
(C++11)(C++11)(C++11) | extracts exponent of the number (function)[edit] |
(C++11)(C++11)(C++11) | extracts exponent of the number (function)[edit] |
(C++11)(C++11) | decomposes a number into integer and fractional parts (function)[edit] |
C documentation forfrexp | |
