C library - ldexp() function

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The C library ldexp() function of type double accepts two parameters say(x and exponent) which returns the result in the form of x multiplied by 2 raised to the power of exponent.

Syntax

Following is the syntax of the C library ldexp() function −

double ldexp(double x, int exponent)

Parameters

This function accepts two parameters −

• x − This is the floating point value representing the significand.

• exponent − This is the value of the exponent.

Return Value

This function returns x * 2 ^exp.

Example 1

Following is the basic C library program to see the illustration of ldexp() function.

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

int main () {
   double x, ret;
   int n;

   x = 0.65;
   n = 3;
   ret = ldexp(x ,n);
   printf("%f * 2^%d = %f\n", x, n, ret);
   
   return(0);
}

Output

The above code produces the following result−

0.650000 * 2^3 = 5.200000

Example 2

Below the program calculate the volume of a sphere using mantissa and exponent.

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

double sphere_volume(double radius) {
   int expo;
   double mantissa = frexp(radius, &expo);

   // Calculate volume = (4/3) *  * (mantissa * 2^exponent)^3
   double vol = (4.0 / 3.0) * M_PI * pow(ldexp(mantissa, expo), 3);

   return vol;
}

int main() {
   double sphere_radius = 5.0; 
   double sphere_vol = sphere_volume(sphere_radius);

   printf("Volume of sphere with radius %.2lf = %.6lf\n", sphere_radius, sphere_vol);
   return 0;
}

Output

On execution of above code, we get the following result −

Volume of sphere with radius 5.00 = 523.598776

Example 3

To get the approximate value of 2^x can use two function − frexp() that return the value of mantissa and for returning the result has used ldexp().

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

double my_power_of_two(double x) {
   int expo;
   double mantis = frexp(x, &expo);
   return ldexp(mantis, expo);
}

int main() {
   double x = 3.96; 
   double approx_power_of_two = my_power_of_two(x);
   printf("Approximate 2^%.2lf = %.6lf\n", x, approx_power_of_two);
   return 0;
}

Output

After executing the above code, we get the following result −

Approximate 2^3.96 = 3.960000