This commit addresses a challenge explained in an open question ("How
can we incorporate correlation in unknown bits across partial
products?") left by Harishankar et al. in their paper:
https://arxiv.org/abs/2105.05398

When LSB(a) is uncertain, we know for sure that it is either 0 or 1,
from which we could find two possible partial products and take a
union. Experiment shows that applying this technique in long
multiplication improves the precision in a significant number of cases
(at the cost of losing precision in a relatively lower number of
cases).

This commit also removes the value-mask decomposition technique
employed by Harishankar et al., as its direct incorporation did not
result in any improvements for the new algorithm.

Signed-off-by: Nandakumar Edamana <[email protected]>