### 3. Library calls (functions within program libraries)

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# FREXP

Section: Linux Programmer's Manual (3)
Updated: 2017-09-15

## 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);
```

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 versions <= 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 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, 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)

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
EXAMPLE
Program source
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