frexp man page

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.

Return Value

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

Conforming to

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

Program source

#include <math.h>
#include <float.h>
#include <stdio.h>
#include <stdlib.h>

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);

See Also

ldexp(3), modf(3)


This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

ldexp(3), modf(3).

The man pages frexpf(3) and frexpl(3) are aliases of frexp(3).

2017-09-15 Linux Programmer's Manual