Eliminating Needless Calculations on Circuit Level: Most-Significant-Digit-First Digit-Serial Processing

l. Introduction In various kinds of information processing, a lot of compare operations are executed on results of arithmetical operations. And this Upe of operation, combination of arithmetical operations and comparisons, often limits the system performance. In such an operation, the outcome is very simple: "tllle" or "false". So precise arithmetical operations are not necessary if correct judgement is guaranteed. -From this point of view, a conventional hardware carries out a large amount of needless calculations, because lower-digit-calculations which have no impact on outcome of comparison are inevitably executed. Motion estimation of video coding, for example, most of the distances are not necessary to be calculated precisely, because those distances are much larger than the minimum one and distance calculations on a few higher digits are enough to complete correct comparison. In other words, most of the calculations on lower digits are needless. However, precise and all-digit calculations are carried out in conventional hardware, deteriorating system performance. In this paper, we will propose a novel technique to remove this wastefulness by calculating and comparing simultaneously from the uppermost digit: most-significantdigit-first (MSD-first) digit-serial processing. To evaluate effectiveness of this technique, we will also present a vector quantization (VQ) processor employing this technique.