2. The Processor Flags (Condition Codes)

• Processor status is described as condition codes, or status flags.

• Condition codes refer to the information about most recently executed instruction.

• For example, if decrementing a register produces zero value, the zero flag ZF is set by the processor.

  • (A programmer might say: zero condition has occurred.)

• Each flag is a single bit in the flag register, EFLAGS.

• If last addition or subtraction produced a negative result, the sign flag SF is set.

• Sign flag SF is equal to the high-order bit of the result of an operation:

  • 0 is positive,

  • 1 is negative.