User:Eevee/Sqrt

This ACS function may be used in a script.

int Sqrt(int number)

fixed FixedSqrt(fixed number)

• number — Value to take the square root of.

Returns the square root of an integer or fixed point number. The integer version returns the floor of the square root, so Sqrt(99) produces 9.

Manual calcuation

In older versions of ZDoom, this function is not built into ACS, so here are several manual equivalents. Do note that for the distance between two objects, the distance function can be faster. Also note that if you name a function sqrt, your code will no longer compile with later versions of ACC.

This version uses Newton's method, where the solution converges quadratically from the initial guess. This function has been compared with the following two, and is at least 5 to 10 times faster in normal use.

function int sqrt(int number)
{
	if(number <= 3) { return number > 0; }

 	int oldAns = number >> 1,                     // initial guess
	    newAns = (oldAns + number / oldAns) >> 1; // first iteration

	// main iterative method
	while(newAns < oldAns)
	{
		oldAns = newAns;
		newAns = (oldAns + number / oldAns) >> 1;
	}

	return oldAns;
}

This is a simpler, but slower, version of a square root function. It rounds the root up or down.

function int sqrt (int x)
{
	int r;
	x = x + 1 >> 1;
	while (x > r)
		x -= r++;
	return r;
}

If you need a function that rounds down, this one will work. Based off of this algorithm.

function int isqrt (int n)
{
	int a;
	for (a=0;n>=(2*a)+1;n-=(2*a++)+1);
	return a;
}

This sample-based formulae processes fixed values and returns a fixed result which accuracy is defined by the samples integer, and results zero if the input number is negative.

function int sqrt(int number) 
{ 
    int samples=15; //Samples for accuracy

    if (number == 1.0) return 1.0; 
    if (number <= 0) return 0;
    int val = samples<<17 + samples<<19; //x*10 = x<<1 + x<<3
    for (int i=0; i<samples; i++) 
        val = (val + FixedDiv(number, val)) >> 1;
 
    return val; 
}

This is the same as above, but optimised for 15 samples.

function int sqrt(int number) 
{
  if (number == 1.0) return 1.0; 
  if (number <= 0) return 0;
  int val = 150.0;
  for (int i=0; i<15; i++) 
    val = (val + FixedDiv(number, val)) >> 1;

  return val; 
}