if($x_dist<0){
$x_dist = -$x_dist;
}
if($y_dist<0){
$y_dist = -$y_dist;
}
$distance = $x_dist+$y_dist;

if($x_dist<0){
$x_dist *=-1;
}
if($y_dist<0){
$y_dist *=-1;
}
$distance = $x_dist+$y_dist;

Creating a fast PHP code is more a matter of knowing how PHP translate the code, seek for variables in his dictionary, reserve and release memory…

It would be interesting to run your PHP tests under HIP HOP PHP or APC cache.

If you write the code in ASM and do it right, computing manathan distance is times faster than just parsing PHP version of the code.

To finish this kind of code is just bad
if($x_dist<0){
$x_dist *=-1;
}
It require a conditional JMP and a multiplication where you just need to set the sign bit of the variable $x_dist to positive.

Emanuele’s method of squaring the distance you want instead of sqrting the measured distance is the fastest IMO (only 3 multiplications and one addition)

With collision response, you can either calculate response with vectors or trig. Trig is just wayyy too cpu expensive, so most people use vectors.

When you use vectors, to calculate the unit vector, you NEED the magnitude (distance), not the magnitude squared. So i tried to find a fast way to calculate the sqrt.

I got this. Its the newton method; very fast and the number of significant figures DOUBLES with every loop.

function sqrt(n)

a = guess

for (accuracy) {
a = 0.5(a + (n/a))
}

return a

Generally, the precompiled Math.sqrt is faster than this for general squareroots, since this is the method it uses =)

But, if you have a tile-based game, or broadphase quadtrees, or grids, the ability to guess and determine accuracy really lowers CPU load. Thats because the computer automatically guesses 1, but since you know the squares apart, you can give a much better guess. Also, you generally don’t need 16bit precision. 3 loops on this will give 8 significant figures, (with a good guess), which is more than anyone needs.

Try it!

For tile-based games the Taxicab is the right one, if you like to get the real distance you need the euclidean-algo.

Maybe I´m wrong, because I can´t believe that you all ignore the fact, that you can´t compare them.

if($valx*$valy<0)
{
$distance=$valx-$valy;
}
else
{
$distance=$valx+$valy;
}

tested on php and actionscript.
The result may be a positive or negative number but that is not a problem since you can check your distance like (-$dist<$distance<$dist).

Could this difference be an issue based on how these two languages are compiled?