Question

I saw this in some JS code:

        index = [
            ascii[0] >> 2,
            ((ascii[0] & 3) << 4) | ascii[1] >> 4,
            ((ascii[1] & 15) << 2) | ascii[2] >> 6,
            ascii[2] & 63
        ];

I’d quite like to know what a lot of this means. Specifically “>>”, a single pipe “|” and the “&” symbol on the last line?

Much appreciated!

Answer 1

x >> y means to shift the bits of x by y places to the right (<< to the left).

x | y means to compare the bits of x and y, putting a 1 in each bit if either x or y has a 1 in that position.

x & y is the same as |, except that the result is 1 if BOTH x and y have a 1.

Examples:

#left-shifting 1 by 4 bits yields 16
1 << 4 = b00001 << 4 = b10000 = 16

#right-shifting 72 by 3 bits yields 9
72 >> 3 = b1001000 >> 3 = b1001 = 9

#OR-ing 
8 | 2 = b1000 | b0010 = b1010 = 10

#AND-ing
6 & 3 = b110 & b011 = b010 = 2

For more information, search Google for “bitwise operators”.