| 摘要 |
<p>Using a subtraction without borrow operation, the first operand lowest order word is subtracted from a second operand lowest order word. If the result of the subtracting is not zero, then a zero (Z) flag is cleared such that a Z flag status is not set. If, however, the result of the subtracting is zero, then the Z flag is set as usual. Next, a first operand next higher order word is subtracted from a second operand next higher order word using a subtraction withborrow and a sticky not Z flag (SBBZ) instruction and, based upon the subtracting, the Z flag is updated accordingly such that it represents the result of the whole multi-word subtraction until the first operand highest order word is subtracted from the second operand highest order word. The comparing of the first operand and the second operand is then based upon the Z flag status, if needed, after the subtraction of the first operand highest order word is subtracted from the second operand highest order word.</p> |
