Abraham R Torres

US Patent:

46850783, Aug 4, 1987

Filed:

Oct 31, 1984

Appl. No.:

6/666703

Inventors:

Abraham Torres - Austin TX

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

G06F 750

US Classification:

364770

Abstract:

A "lookback" carry function is implemented in a binary incrementor. In contrast to conventional lookahead carry functions, the present "lookback" carry function implements an actual carry during the incrementing operation. After the carry function has been implemented at each register position, a subsequent determination is made as to whether each carry function was a valid one and should have been carried out. With respect to any carry functions which were not valid, subsequent circuitry will eliminate such carries to leave the appropriate carry pattern in each position of the register. In order for a carry to be considered valid, the incrementation of all bits of a lower order must have resulted in a carryout.