frexp(3)

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

LIBRARY
Math library (libm, -lm)

SYNOPSIS
#include <math.h>

double frexp(double x, int *exp);
float frexpf(float x, int *exp);
long double frexpl(long double x, int *exp);

    Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

frexpf(), frexpl():
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
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.

ERRORS
No errors occur.

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

STANDARDS
C11, POSIX.1-2008.

HISTORY
C99, POSIX.1-2001.

The variant returning double also conforms to SVr4, 4.3BSD, C89.

EXAMPLES
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 <float.h>
    #include <math.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, 2, exp, x);
        exit(EXIT_SUCCESS);
    }

SEE ALSO
ldexp(3), modf(3)