frexp (3)

Leading comments

Copyright 1993 David Metcalfe (david@prism.demon.co.uk)

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Sin...

(The comments found at the beginning of the groff file "man3/frexp.3".)

NAME

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

SYNOPSIS

#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():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

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
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.

EXAMPLE

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>

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);
}

SEE ALSO

ldexp(3), modf(3)

COLOPHON

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