Assembly - The sign flag & parity flag

Question

I didn\'t understand when the sign flag is set, and when the parity.

As I know, the sign flag indicates the sign of the result of an operation, 0 for positive numbers an

Answer 1

The code

mov al, -5 
sub al, 124

calculates 256-5-124. It's 127 and it's positive number

Both sub al, al and 127+129 evaluates to 0, it has 0 bits set, and 0 is even value, so PF is set.