We present an enumerative technique for encoding and decoding of dc-free runlength-limited sequences. The size of the full-precision weight set required for implementing the presented coding scheme is about the same as required for implementing the enumerative coding scheme for pure dc-free sequences presented by Immink in 1991. Using finite-precision floating point notation to express the weight coefficients, the presented coding technique enables the implementation of channel encoders and decoders of moderate complexity. Practically interesting dc-free RLL modulation codes can be implemented which approach the maxentropic bounds very closely in terms of code rate and low-frequency suppression capability. The hardware required for implementing such a quasi-maxentropic scheme mainly consists of a ROM of size at most 5 kByte.

Key Words: enumerative coding, constrained code, recording code, run-length-limited