Struct BitPackCompactor 

pub struct BitPackCompactor<W: Semiring> { /* private fields */ }

Bit-packing compactor for FSTs with small label/state spaces

BitPackCompactor achieves high compression ratios by packing multiple fields into fixed-size integers when the FST has limited label alphabets and state counts. This strategy is ideal for phoneme FSTs, character-based automata, or any FST where labels and state IDs fit in small bit widths.

Compression Approach

Packs arc data into 64-bit integers using a configurable bit layout:

• Configurable bits for ilabel (e.g., 16 bits for 65K symbols)
• Configurable bits for olabel
• Configurable bits for nextstate
• Remaining bits for quantized weight

Usage Example

use arcweight::prelude::*;
use arcweight::fst::{CompactFst, BitPackCompactor};

// Configure for ASCII FST (7-bit labels, 10-bit states)
let compactor = BitPackCompactor::<TropicalWeight>::new(7, 7, 10);
let fst = CompactFst::with_compactor(compactor);

Implementations

impl<W: Semiring> BitPackCompactor<W>

pub fn new(ilabel_bits: u8, olabel_bits: u8, state_bits: u8) -> Self

Create a new bit-packing compactor with specified bit widths

Parameters

• ilabel_bits: Bits for input labels (max 32)
• olabel_bits: Bits for output labels (max 32)
• state_bits: Bits for state IDs (max 32)

Panics

Panics if total bits exceed 64 or any field exceeds 32 bits

Trait Implementations

impl<W: Clone + Semiring> Clone for BitPackCompactor<W>

fn clone(&self) -> BitPackCompactor<W>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<W: Semiring> Compactor<W> for BitPackCompactor<W>

where W::Value: WeightConverter<W::Value> + Copy,

type Element = u64

Compressed element type that stores arc or weight data

fn compact(&self, arc: &Arc<W>) -> Self::Element

Compress an arc into the compact element format

fn expand(&self, element: &Self::Element) -> Arc<W>

Expand a compressed element back into a full arc

fn compact_weight(&self, weight: &W) -> Self::Element

Compress a semiring weight into the compact element format

fn expand_weight(&self, element: &Self::Element) -> W

Expand a compressed element back into a semiring weight

impl<W: Debug + Semiring> Debug for BitPackCompactor<W>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<W: Semiring> Default for BitPackCompactor<W>

fn default() -> Self

Returns the “default value” for a type.