faster sqrt function for marlin in planner.ccp

thingiverse

In the given C++ code, "SqrtAprox" is an alternate function that approximates the square root of a number and increases its calculation speed by 300%. This alternative planner.ccp file can potentially enhance the performance of planner.ccp, but it's experimental and may contain errors up to 3.5% for integers. The method is inspired by hacking techniques used in the Quake III engine for lighting calculations. Replacing the marlin firmware with this file can free up processing power on Arduino during acceleration, allowing for more advanced LCD graphics in the future. An image comparison shows a side-by-side view of results achieved with the new and old planner.ccp files. Please refer to [http://forums.reprap.org/read.php?147,219210](http://forums.reprap.org/read.php?147,219210) for more information on the method and its implementation. To use this, simply replace the existing marlin planner.ccp file with the provided alternate version.