13.2    PARALLEL MULTIPLIERS

This section considers multipliers that can perform two’s complement multiplication in time O(W) using regular structures, including multiplication with sign extension (derived from Horner’s rule) and Baugh-Wooley multiplication [9]. Two regular implementation styles, carry-ripple and and carry-save array, are introduced.

It has been proved that multiplications cannot be performed in a time smaller than O(log2W). Such a bound is attainable by the binary-tree and Wallace-tree multipliers (see Appendix E) [10]. However, their corresponding architectures are very irregular.

Let the multiplicand and multiplier be A and B:

image

where −1 < A, B < 1 and the case when both A and B is equal to −1 is excluded. The value of their product P = A × B is given by:

image

where the radix point is to the right of the msb p2w−2. Since the product of 2 numbers within [−1, 1) is also in this range, all higher order bits to the left of bit-position 2W − 2 in the result are ignored.

In constant wordlength multiplication, the W − 1 lower order bits in the product P are discarded, and the product is denoted as XP = A × B, where

image

The product X is used when a constant wordlength multiplier ...

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