| 摘要 |
PURPOSE:To prevent redundant calculation and to improve the practical arithmetic processing speed of a variable-length data, by checking the number of effective figures of the 2nd operand and performing the precheck of overflow by using the checked result. CONSTITUTION:An Reg II (the number of effective figures of the 2nd operand) selected by a selector 33 and an L1*2 (which is obtained by shifting L1 data leftward by one bit) selected by another selector 34 are inputted into an adder- subtracter 35. When the subtraction result of L1*2-Reg II is 0 (zero) or negative, it is judged that overflow occurs. In case where it is judged that overflow occurs, the calculation is not executed by a calculating section and a condition code indicating overflow is produced by treating the calculation as processing- terminated one. On the other hand, when no overflow is judged as a result of the calculation, arithmetic of (the 1st operand + one digit) is executed by the arithmetic section. |
