C # shift operator

Question

Here is an expression written by my colleague that I do not quite understand. Unfortunately, it is not available right now, so here it is (with the changed names, we are working on a game in Unity).

private readonly int FRUIT_LAYERS = (1 << LayerMask.NameToLayer("Apple")) | (1 << LayerMask.NameToLayer("Banana")); 

NameToLayer takes a string and returns an integer. I have always seen left shift operators used with a constant integer on the right, and not on the left, and all the examples that I find using Google follow this approach. In this case, I think that he was pushing Apple and Banana to the same relative layer (which I will use later for filtering). There will be more “fruits” to filter in the future. Any brilliant stackoverflowers that can give me an explanation of what happens on these lines?

Answer 1

Your colleague essentially uses int instead of bool[32] to try to save space. The code block that you show is similar

 bool[] FRUIT_LAYERS = new bool[32]; FRUIT_LAYERS[LayerMask.NameToLayer("Apple")] = true; FRUIT_LAYERS[LayerMask.NameToLayer("Banana")] = true; 

You might want to consider a template like this:

 [Flags] enum FruitLayers : int { Apple = 1 << 0, Banana = 1 << 1, Kiwi = 1 << 2, ... } private readonly FruitLayers FRUIT_LAYERS = FruitLayers.Apple | FruitLayers.Banana; 

Answer 2

1 << x essentially says "give me a number, where the (x + 1) -th bit is one, and the rest of the numbers are zero.

x | y x | y is a bitwise OR, so it will go through each bit from 1 to n, and if this bit is one of x or y , then this bit will be one of the results if it is not equal to zero.

So, if LayerMask.NameToLayer("Apple") returns 2 and LayerMask.NameToLayer("Banana") returns 3 , then FRUIT_LAYERS will be the number with 3rd and 4th bits, which is 1100 in binary format, or 12 in the database ten.

Answer 3

The code shifts the binary value 1 to the left, the number of binary shift places is determined by Apple and Banana, after shifting both ORed values ​​in binary

Example: Suppose an apple returns 2 and 3 banana returns you get: 1 <2, which is 0100 (which means 4 in decimal) 1 <3, which is 1000 (this means eight in decimal)

now 0100 bitwise or from 1000 is 1100, which means 12

Answer 4

1 <n is basically equivalent to 2 ⁿ