write-compressor

To implement a compatible arithmetic coding encoder, you must match renormalization timing, byte-output formulas, and probability model updates exactly. Reimplement the decoder as a simulator to trace state transitions and derive the exact byte-output formulas.

State divergence occurs when encoder and decoder probability model updates or renormalization timing mismatch. Prevent this by maintaining dual simulators, comparing step-by-step debug traces, and adding unit tests asserting state synchronization after every operation.

Start incremental implementation with single-bit and single-integer encoders, verify them against a decoder simulator, extend to sequences, and only then attempt full-file compression to ensure interoperability with the existing arithmetic decoder.

Write decoder-simulator unit tests that assert state synchronization after every operation. Maintain both encoder and decoder simulators, compare step-by-step debug traces for fraction, range, and low values, and verify decoded output matches exactly.

Yes, this approach specifically targets legacy archives that must interoperate with an existing arithmetic decoder. By deriving exact byte-output formulas through decoder-first analysis, you prevent the subtle state divergence that causes data corruption.

Yes, the implementation applies to bit-level encoders and incremental encoder development for single bits up to full-file compression. You start with a minimal encoder that encodes a single bit and verify state and decoded output match exactly.