ldexp(), ldexpf(), ldexpl()

Updated: April 19, 2023

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
The general-purpose math library.
libm-sve
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

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

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

Returns:

x * 2exp

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:

C11, POSIX 1003.1

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