frexp(), frexpf(), frexpl()

Break a floating-point number into a normalized fraction and an integral power of 2

Synopsis:

#include <math.h>

double frexp( double value, 
              int* exp );

float frexpf( float value, 
              int* exp );

long double frexp( long double value, 
                   int* exp );

Arguments:

value: The value you want to break into a normalized fraction.
exp: A pointer to a location where the function can store the integral power of 2.

Library:

libm

Use the -l m option to qcc to link against this library.

Description:

These functions break a floating-point number into a normalized fraction and an integral power of 2. It stores the integral power of 2 in the int pointed to by exp.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Call feclearexcept(FE_ALL_EXCEPT) before calling frexp(), frexpf(), or frexpl().
On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

A number, x, that has a magnitude in the interval [0.5, 1.0] or is 0.0, such that value = x * 2^exp.

If `value` is:	These functions return:	*`exp`	Errors:
±0.0	0.0, with the same sign as `value`	0	—
±Inf	`value`	Unspecified	—
NaN	`value`	Unspecified	—

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Examples:

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

int main( void )
{
    int expon;
    double value;
    int except_flags;

    feclearexcept(FE_ALL_EXCEPT);
    value = frexp(  4.25, &expon );
    printf( "%f %d\n", value, expon );
    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    feclearexcept(FE_ALL_EXCEPT);
    value = frexp( -4.25, &expon );
    printf( "%f %d\n", value, expon );
    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    return EXIT_SUCCESS;
}

produces the output:

0.531250 3
-0.531250 3

Classification:

ANSI, POSIX 1003.1

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	No
Thread	Yes