「操作系统」：The most useful condition codes

CF: Carry Flag.The most recent operation generated a carry out of the most significant bit. Used to detect overflow for unsigned operations.

ZF: Zero Flag. The most recent operation yielded zero.

SF: Sign Flag. The most recent operation yielded a negative value.

OF: Over Flag. The most recent operation caused a two's-complement overflow----either negative or positive

　　For example, suppose we used one of the ADD instructions to perform the equivalent of the C assignment t = a+b, where variables a, b and t are integers. Then the condition codes would be set according to the following C expressions:

CF:　　　　(unsigned) t < (unsigned) a　　　　Unsigned overflow

ZF:　　　　(t == 0)　　　　　　　　　　　　　Zero

SF:　　　　(t < 0)　　　　　　　　　　　  　　Negative

OF:　   　　(a < 0 == b < 0) && (t < 0 != a < 0)　Signed overflow