Optimized binary adders and comparators for inputs having different widths
US5517440A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 2, 1995 |
| Grant date | May 14, 1996 |
| Priority date | — |
| Expiry date | May 2, 2015 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06F2207/3816
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
A first two-input adder computes the sum of one wider and one narrower input by combining a conventional adder for the low-order bits with an incrementer and selection logic for the high-order bits. A second three-input adder computes the sum of one wider and two narrower inputs in a similar way: the low-order bits are computed with a conventional carry save adder (CSA) followed by a carry propagate adder (CPA), while the high-order bits are computed with an incrementer and selection logic. The first and second circuits are combined to form a third arithmetic circuit that takes four input operands, the first of which is wider than the other three, and speculatively computes two results: (1) the sum of the first and second input operands; and (2) the sum of the first, third, and fourth input operands. This combined circuit contains all of the elements of the first two circuits, but shares a single incrementer. A degenerate case of the third circuit occurs when the second and third inputs are common. This degenerate case has particular application to superscalar instruction pointer updates for variable length instructions. By taking into account a priori restrictions on the possible …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.