I have a sample problem with w=1, y=7, z=0, x = ~(w && y) | y; and the solution is x = -1, but I can't figure out why?
Here is my thought process:
(w && y) = (1 && 7) = 1
~1
1 in bits is 0000 0001
~1 in bits is 1111 1110
Not sure what to do from here.
The last step is a bitwise OR so you get:
1111 1110 | 0000 0111 = 1111 1111
which is -1.
~1 in bits is 1111 1110,
1111 1110 or 0000 0111 is 1111 1111,
and 1111 1111 is -1. The most significant bit is the negative flag, and negative numbers are subtractive, I guess you could say. That's why a signed byte can hold down to -128 but only up to 127.
You're right that ~(w && y) gives 1111...0. The last bit of 7 is 1, so |ing this with 7 gives 1111...1, or -1.
First, you should be using & instead of && for bitwise operations. Second, after ~1 = 111...1110 is calculated, it is ORed with y (7) to get 1111..1111, the 2's-complement representation of -1.
1111 1110ored with111?(1111 1110) | y.