Data recording or transmission system using run length limited coding.

摘要

The invention concerns a data recording or transmission system using run length limited coding. In such a system a length oriented arithmetic decoder (3) constrained to ONE-TO-ONE map in the data string to run length limited string direction and ONTO map in the run length limited to data string direction through an arithmetic encoder (9) preserves the fixed rate of the RLL string and ensures representability. A finite state machine responsive to the arithmetic decoder output provides the trial augends and shift amounts necessary for the magnitude comparison decoding of the data string treated as if it were arithmeticaily compressed. A finite state machine is also used with the arithmetic encoder for providing trial augends and shift amounts but is responsive to successive RLL symbols as if it were ordinary source strings. The encoder combines the augends with a predetermined retained portion of the generated data string. The ONTO mapping assures that RLL strings do not map into arithmetic strings which have no RLL string counterparts and which arise out of the nature of recursive arithmetic compression coding while the ONE-TO-ONE mapping assures the existence of an RLL string for each data string. Significantly, the length of the code string is the product of the code string duration times its fixed state. This is independent of encoder/decoder state.