Multiply and divide by shift

[SiwenFeng]

In general, multiply or divide by an integer can get the result by shifting it. The multiply and divide method - generate left-shifted code if multiply by 2n, and multiply by any other integer or divide by any number. The shift method is more efficient than the multiplication and division method.

[gurushida]

One of the goal of this project is to be as easy to understand as possible. Even in the case of a compiler not smart enough to generate the fastest code anyway, replacing a "/4" by ">>2" makes the code less readable, so unless this happens in a performance critical code path (like the animation loop of a 3D rendering engine), which is not the case here, I prefer readability.

Besides, if for some reason you really need to optimize this code as much as you can, adding -O3 to the Makefile and looking at ways to do some operations like polynomial calculations without reallocating intermediate objects is likely to make a much bigger difference than a division.