nx_range_coef.nx

nx_range_coef.nx -- adaptive order-0 byte model wrapper around nx_range_coder, sized for the post-RLE coefficient stream. The post-zigzag-RLE byte stream is highly skewed: most run-bytes are small (the longest runs are bounded by 63), and most level- bytes are small (low magnitude after quantisation). An adaptive frequency table tracks the distribution within the message and asks the arithmetic coder for sub-byte symbol widths -- the compounding compression step on top of zigzag + RLE. Adaptation policy: each encoded byte bumps its frequency by 8; after total > 16384 we halve all frequencies (decay to prevent the model from over-committing to the early bytes of the stream). genealogy_id: rissanen_1976_arithmetic_coding + witten_neal_cleary_1987_arithmetic_coding_for_data_compression + nx_range_coder_q10 lineage_id: nishi_range_coef_q10