Defined in header <cmath> | ||
---|---|---|
float frexp( float arg, int* exp ); | (1) | |
double frexp( double arg, int* exp ); | (2) | |
long double frexp( long double arg, int* exp ); | (3) | |
double frexp( Integral arg, int* exp ); | (4) | (since C++11) |
arg
into a normalized fraction and an integral power of two. double
).Parameters
arg | - | floating point value |
exp | - | pointer to integer value to store the exponent to |
Return value
If arg
is zero, returns zero and stores zero in *exp
.
Otherwise (if arg
is not zero), if no errors occur, returns the value x
in the range (-1;-0.5], [0.5; 1)
and stores an integer value in *exp
such that x×2(*exp)
=arg.
If the value to be stored in *exp
is outside the range of int
, the behavior is unspecified.
If arg
is not a floating-point number, the behavior is unspecified.
Error handling
This function is not subject to any errors specified in math_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
- If
arg
is ±0, it is returned, unmodified, and0
is stored in*exp
. - If
arg
is ±∞, it is returned, and an unspecified value is stored in*exp
. - If
arg
is NaN, NaN is returned, and an unspecified value is stored in*exp
. - No floating-point exceptions are raised.
- If
FLT_RADIX
is 2 (or a power of 2), the returned value is exact, the current rounding mode is ignored
Notes
On a binary system (where FLT_RADIX
is 2
), frexp
may be implemented as.
{ *exp = (value == 0) ? 0 : (int)(1 + std::logb(value)); return std::scalbn(value, -(*exp)); }
The function std::frexp
, together with its dual, std::ldexp
, can be used to manipulate the representation of a floating-point number without direct bit manipulations.
Example
Compares different floating-point decomposition functions.
#include <iostream> #include <cmath> #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 + 0.45 frexp() makes 0.964453 * 2^7 logb()/ilogb() make 1.92891 * 2^6
See also
multiplies a number by 2 raised to a power (function) | |
(C++11) | extracts exponent of the number (function) |
(C++11) | extracts exponent of the number (function) |
decomposes a number into integer and fractional parts (function) | |
C documentation for frexp |
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