#include <stdio.h>

float Q_rsqrt(float);

main()

{

	float number, result;

	printf("Enter number: ");

	scanf(" %f", &number);

	result = Q_rsqrt(number):

	printf("Inverse square root: %f", result);

}

float Q_rsqrt( float number )

{

	long i;

	float x2, y;

	const float threehalfs = 1.5F;



	x2 = number * 0.5F;

	y  = number;

	i  = * ( long * ) &y;                       // evil floating point bit level hacking

	i  = 0x5f3759df - ( i >> 1 );               // what the ... ?

	y  = * ( float * ) &i;

	y  = y * ( threehalfs - ( x2 * y * y ) );   // 1st iteration

//	y  = y * ( threehalfs - ( x2 * y * y ) );   // 2nd iteration, this can be removed

	return y;

}