msrtc-rans

Safe public Rust entropy-coder API for msrtc_rans.

This crate provides the high-level entropy coder API, wrapping the raw rANS primitives from msrtc-rans-core with PMF validation, CDF table construction, bypass coding, and distribution descriptors.

Status — Phase 3 Sealed ✅

The full entropy encode/decode pipeline (PMF → CDF → bypass) has been verified byte-for-byte against the pinned Microsoft C++ oracle. All 30 entropy tests plus 1 doc-test pass.

Features

• #![forbid(unsafe_code)] — pure safe Rust
• Both RansByte (u8) and Rans64 (u32) variant support
• PMF validation: rejects empty tables, invalid dimensions, zero frequencies
• Bypass coding for out-of-range values with configurable bypass bits
• Mixed in-range and bypass value streams
• Comprehensive error handling via EntropyError enum
• Re-exports all msrtc-rans-core types and traits

Usage

Entropy Encoding/Decoding

use msrtc_rans::entropy::EntropyEncoder;
use msrtc_rans_core::RansByte;

let mut encoder = EntropyEncoder::<RansByte>::new();

let pmf_lengths = vec![2u32];
let pmf_offsets = vec![0u32];
let pmf_table = vec![1u32, 3u32];  // frequencies
let symbol_bits = 16;
let bypass_bits = 4;

encoder.initialize(&pmf_lengths, &pmf_offsets, &pmf_table, symbol_bits, bypass_bits)
    .expect("valid PMF");

let values = vec![-2i32, 1i32, 0i32, 1i32];
let encoded = encoder.encode(&values).expect("encode");

// Decode
use msrtc_rans::entropy::EntropyDecoder;
use msrtc_rans_core::RansByte;

let mut decoder = EntropyDecoder::<RansByte>::new();
decoder.initialize(&pmf_lengths, &pmf_offsets, &pmf_table, symbol_bits, bypass_bits)
    .expect("valid PMF");

let decoded = decoder.decode(&encoded).expect("decode");
assert_eq!(decoded, values);

Raw rANS (re-exported from msrtc-rans-core)

use msrtc_rans::{RansByteEncoder, RansByteDecoder};
use msrtc_rans::{VecSink, SliceSource};

let sink = VecSink::<u8>::new(64);
let mut encoder = RansByteEncoder::new(sink);
encoder.put_raw(0, 128, 8);
encoder.flush();
let encoded = encoder.into_sink().encoded().to_vec();

let source = SliceSource::new(&encoded);
let mut decoder = RansByteDecoder::new(source);
assert!(decoder.init());
assert!(decoder.advance(0, 128, 8));
assert!(decoder.check_eof());

Repository

Full project: github.com/infinityabundance/msrtc-rans-rs

License

MIT — see LICENSE and NOTICE for attribution notices.