1. A special-purpose search processor, comprising: a plurality of serially-connected cells, each cell including a pattern register for storing part of a search pattern to be searched for, a character register for storing a character of a data stream to be searched, the character register of each cell being serially connected with character registers of other cells to form a character line, comparator means, connected to the pattern register and the character register, for comparing the contents of the pattern register and the character register, and a first match register for storing a quantity indicative of a match between the search pattern and the data stream, the first match register of each cell being serially connected with first match registers of other cells to form a first match line; means for initializing the cells to contain the search pattern; clock means for gating the data stream from cell to cell in the character line; means for inputting a tolerance value into the first match line, to indicate a degree of mismatch that will be tolerated; match logic means in each cell, including means for generating a match signal upon detection of a match between selected bits of the pattern register and the character register, and means for decrementing the tolerance value carried on the first match line if there is no detected match; at least one additional match register in each cell, serially connected with additional match registers of other cells to form at least one additinal match line; and means within each cell for controlling movement of tolerance values between match lines to effect a selected one of a variety of search functions.