ldexp(), ldexpf(), ldexpl()

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 2exp. A range error may occur.

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

Returns:

x × 2exp

For a correct value that would cause an underflow, these functions return 0.0.

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_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
    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