Method, apparatus and system forming the sum of data in plural equal sections of a single data word

摘要

This invention is a technique for summing plural sections of a single data word. The technique uses a repeated process forming larger and larger partial sums. Initially the single data word is rotated one section. The original single data word and the rotated single data word are masked with a mask having "1's" and "0's" in alternate sections. The mask blocks alternate sections so that adjacent sections of the original data word may be summed on a whole data word basis without any overflow disrupting the partial products. The two masked data words are then summed. This sum results in half as many partial sums as before. Each of these larger partial sums now occupies two original sections of the data word. The process can be repeated for these large partial sums. In the preferred embodiment this technique is used with an arithmetic logic unit (230) capable of forming mixed arithmetic and Boolean combinations of three inputs having a barrel rotator (235) driving one input. The arithmetic logic unit (230) receives the single data word at a first input (241) and the rotated single data word at a second input (241). The mask supplies the third input (243). The arithmetic logic unit (230) then forms the combination (A&C)+(B&C), which is field addition of A and B as masked by C. With proper selection of the mask and the rotate amount, the three input arithmetic logic unit (230) forms the shift, mask and addition in a single cycle. In the preferred embodiment of this invention, the three input arithmetic logic unit (230) is embodied in at least one digital image/graphics processor (71) as a part of a multiprocessor (100) formed in a single integrated circuit used in image processing.