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 \nx\n, int *\nexp\n);\n
\nfloat frexpf(float \nx\n, int *\nexp\n);\n
\nlong double frexpl(long double \nx\n, int *\nexp\n);

frexpf(), frexpl():

\n
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
\n
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
        || /* 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).

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:

$\n ./a.out 2560\n
frexp(2560, &e) = 0.625: 0.625 * 2^12 = 2560
$\n ./a.out -4\n
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[])
{
\n
    double x, r;
\n
    int exp;
\n
    x = strtod(argv[1], NULL);
\n
    r = frexp(x, &exp);
\n
    printf("frexp(%g, &e) = %g: %g * %d^%d = %g\n", x, r, r, 2, exp, x);
\n
    exit(EXIT_SUCCESS);
}

SEE ALSO#

ldexp(3), modf(3)