Computer program for encoding digital data

A computer program stored in an information recording medium for enabling a computer to implement a method of encoding an input bit stream into a stream of output code words according to variable-length encoding rules using a variable constraint length, wherein a maximum value N of the constraint length is equal to or greater than 2, and the output-code-word stream observes prescribed run length limiting rules RLL (d, k), “d” and “k” denoting a predetermined minimum run length and a predetermined maximum run length respectively, the method comprising the steps of:

• preparing M encoding tables in accordance with the variable length encoding rules, M denoting a predetermined natural number equal to or greater than 2;
• periodically inserting a DSV control bit into a first input bit stream at intervals each corresponding to a prescribed number of successive bits in the first input bit stream to change the first input bit stream into a second input bit stream;
• encoding every m-bit piece of the second input bit stream into an n-bit output signal forming at least a portion of an output code word by referring to the M encoding tables, thereby converting the second input bit stream into a first output bit stream composed of output code words and observing the prescribed run length limiting rules RLL (d, k), “m” and “n” denoting predetermined natural numbers respectively;
• inserting a sync word of a predetermined bit pattern into the first output bit stream for every frame to change the first output bit stream into a second output bit stream;
• terminating a frame-end output code word at a position before a next-frame sync word;
• and
• implementing DSV control of the second output bit stream in response to the inserted DSV control bits.