Thread: question about what this line might be trying to accomplish

I'm not entirely sure about this line of code, its from the original gl quake's source code. Carmack does a lot of funny things at the bit level and I have no friggin clue what they are supposed to be

the actual part of this is the
rand()&3) & 1

the entire context is this:
any clue what the bitwise and operator is being used for? If i remember correctly if bit A and bit B are 1, then the resulting bit is also a 1, otherwise its a zero if either are 0?

Code:

	if ( ((rand()&3) & 1) ||  abs(deltay)>abs(deltax))
	{
		tdir=d[1];
		d[1]=d[2];
		d[2]=tdir;
	}

Oh and this is actually monster code, I guess it randomly chooses a dijrection to move in somehow?

Thanks if you can help explain this to me

EDIT: is doing operations on variables faster on the bit level?