CSC258H1 Lecture Notes - Operand, Barrel Shifter, Shift Register
Document Summary
Devised as a way to take advantage of circuits where shifting is cheaper than adding, or where space is at a premium. Based on the premise that when multiplying by certain values (ex. 99) it can be easier to think of this operation as a difference between two products. Consider the shortcut method when multiplying a give demical value x by 9999: Now consider the equivalent problem in binary. This idea is triggered on cases where two neighboring digits in an operand are different. If digits at i and i 1 are 0 and 1, the multiplicand is added to the result at position i. If idigits at i and i 1 are 1 and 0, the multiplicand is subtracted from the result at position i. The result is always a value whose size is the sum of the sizes of the two multiplicands. In worst case this well be as efficient as an accumulator circit.
