Apparatus and system for sum of plural absolute differences

摘要

A method for forming a sum of the absolute value of the difference between each pair of numbers of respective first and second sets of numbers. The method includes forming the difference between corresponding numbers of the first and second sets. This difference is either added to or subtracted from a running sum based upon its sign. This is repeated for all number pairs. Preferably, the initial subtraction sets a status bit in a flag register (211) which controls the selection of addition or subtraction. The conditional addition to or subtraction from the running sum may generate a carry-out representing the most significant bit of the running sum. This carry-out is preferably stored and later added to the running sum to recover the most significant overflow bits. This technique is preferably practiced using an arithmetic logic unit (230) that can be split into plural independent sections (301, 302, 303, 304). A multiple flags register (211) stores status bits of corresponding sections controlling the conditional addition to or subtraction from a like plurality of running sums. After finishing the subtractions of all number pairs, the partial running sums of each section are added to obtain the final desired sum. A set of the carry-outs from the plural subtractions preferably is used as an index into a look-up table having entries equal to the number of "1's" in the index to sum the overflow bits.