Struct Cabac 

pub struct Cabac<'a> { /* private fields */ }

The CABAC decoder: arithmetic engine reading MSB-first from the RBSP plus the 460 adaptive context models.

Implementations

impl<'a> Cabac<'a>

pub fn new( data: &'a [u8], start_byte: usize, qp: i32, init_idc: u32, is_i: bool, ) -> Self

Initializes from the RBSP data at byte offset start_byte (the slice data, byte-aligned past the header), the slice’s qp (clamped 0..51), cabac_init_idc, and whether the slice is I/SI (spec §9.3.1).

pub fn dbg_state(&self) -> (u32, u32)

Engine state (codIRange, codIOffset) — for bring-up verification against the oracle’s symbol 0 (Brick 1.1). At slice start this is (510, first-9-bits).

pub fn pcm_start_byte(&self) -> usize

I_PCM sample position (spec §7.3.5 + §9.3.3.2.5). The PCM marker is a terminate bin; after it decodes as 1, the encoder’s flush output is already inside the engine’s borrowed offset bits, so the raw pcm_sample_* bytes start at the consumed-bit position rounded up to the next byte boundary (pcm_alignment_zero_bits). byte_pos·8 − cnt is that consumed position (offset-field bits count as read, buffered bits do not). Valid only immediately after decode_terminate() returned true (no renormalization has run since).

pub fn reinit_at(&mut self, byte: usize)

Re-initializes the arithmetic engine at absolute byte (spec §9.3.1.2, invoked after the I_PCM samples), KEEPING the adaptive context models — only the engine registers restart. Mirrors the tail of Cabac::new.

pub fn decode_decision(&mut self, ctx_idx: usize) -> u32

Decodes a context-coded bin (spec §9.3.3.2.1), updating the context model. STATE-RESIDENCY REFUTED (WHYS Part 21): this attribute was added on the Part 19 hypothesis that the engine state round-tripped memory per bin through an outlined call. The symbol table refuted it — LLVM already fully inlined this method in the un-attributed build (zero outlined copies in either binary), and the A/B was null as that predicts. The Part 19 ns/bin sizing was also census-tax-inflated: the true engine cost is ~4 ns/bin, and the residual gap vs ffmpeg’s ~2 is the engine’s per-bin WORK (u64-window renorm bookkeeping vs a 16-bit lazy refill), not call overhead. The attribute stays as documentation + insurance.

pub fn decode_bypass(&mut self) -> u32

Decodes a bypass (equiprobable) bin (spec §9.3.3.2.3).

pub fn decode_terminate(&mut self) -> bool

Decodes the terminate bin (spec §9.3.3.2.4); true ends the slice (or marks I_PCM). No renormalization on terminate.