ldexp(), ldexpf(), ldexpl()

Load exponent: multiply a floating-point number by an integral power of 2

Synopsis:

#include <math.h>

double ldexp( double x, 
              int exp );

float ldexp( float x, 
             int exp );

long double ldexpl( long double x,
                    int exp );

Arguments:

x: A floating-point number.
exp: The exponent of 2 to multiply x by.

Library:

libm

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

Description:

These functions multiply the floating-point number x by 2^exp.

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

Call feclearexcept(FE_ALL_EXCEPT) before calling ldexp(), ldexpf(), or ldexpl().
On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

x * 2^exp

If:	These functions return:	Errors:
`x` is ±0.0	`x`	—
`x` is ±Inf	`x`	—
`x` is NaN	`x`	—
The result would cause overflow	Inf	FE_OVERFLOW
The correct value would cause underflow	The correct value, after rounding	—

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

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

    feclearexcept(FE_ALL_EXCEPT);

    value = ldexp( 4.7072345, 5 );

    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    printf( "%f\n", value );

    return EXIT_SUCCESS;
}

produces the output:

150.631504

Classification:

ANSI, POSIX 1003.1

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