This version of this document is no longer maintained. For the latest documentation, see http://www.qnx.com/developers/docs.

ldexp(), ldexpf()

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 );

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.

A range error may occur.

Returns:

x * 2^exp

If an error occurs, these functions return 0, but this is also a valid mathematical result. If you want to check for errors, set errno to 0, call the function, and then check errno again. These functions don't change errno if no errors occurred.

Examples:

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

int main( void )
{
    double value;

    value = ldexp( 4.7072345, 5 );
    printf( "%f\n", value );
    
    return EXIT_SUCCESS;
}

produces the output:

150.631504

Classification:

ANSI, POSIX 1003.1

See also:

frexp(), modf()