FREXP(3) Linux Programmer's Manual FREXP(3)

frexp, frexpf, frexpl - convert floating-point number to fractional and integral components

#include <math.h>
double frexp(double x, int *exp);
float frexpf(float x, int *exp);
long double frexpl(long double x, int *exp);
Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
frexpf(), frexpl():
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

These functions are used to split the number x into a normalized fraction and an exponent which is stored in exp.

These functions return the normalized fraction. If the argument x is not zero, the normalized fraction is x times a power of two, and its absolute value is always in the range 1/2 (inclusive) to 1 (exclusive), that is, [0.5,1).
If x is zero, then the normalized fraction is zero and zero is stored in exp.
If x is a NaN, a NaN is returned, and the value of *exp is unspecified.
If x is positive infinity (negative infinity), positive infinity (negative infinity) is returned, and the value of *exp is unspecified.

No errors occur.

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
frexp (), frexpf (), frexpl () Thread safety MT-Safe

C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.

The program below produces results such as the following:

$ ./a.out 2560
frexp(2560, &e) = 0.625: 0.625 * 2^12 = 2560
$ ./a.out -4
frexp(-4, &e) = -0.5: -0.5 * 2^3 = -4

#include <math.h>
#include <float.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]) { double x, r; int exp;
x = strtod(argv[1], NULL); r = frexp(x, &exp);
printf("frexp(%g, &e) = %g: %g * %d^%d = %g\n", x, r, r, FLT_RADIX, exp, x); exit(EXIT_SUCCESS); }

ldexp(3), modf(3)