coder.js

export function decode(inp, prediction, min_bits = 16) {
    const out = [];
    let bottom = 0;
    let top = 0;
    let bits = 0;
    let acc = 0;
    let i = 0;
    let consumed = 0;

    while (top - bottom + 1 > 2 ** (i - inp.length + 1)) {
        const bits_to_add = Math.max(min_bits - (top + 1 - bottom).toString(2).length + 1, 0);
        bottom *= 2 ** bits_to_add;
        top = (top + 1) * 2 ** bits_to_add - 1;
        const l = Math.max(Math.min(inp.length - i, bits_to_add), 0);
        acc = acc * 2 ** l + from_bin(inp.slice(i, i + l));
        acc *= 2 ** (bits_to_add - l);
        i += bits_to_add;
        bits += bits_to_add;
        const ranges = prediction(out).reduce((acc, x) => {
            acc.push((acc[acc.length - 1] || bottom) + Math.floor(x * (top + 1 - bottom) / acc[acc.length - 1]));
            return acc;
        }, []);
        const x = ranges.findIndex((range) => range > acc);
        out.push(x);
        ranges.unshift(bottom);
        bottom = ranges[x];
        top = ranges[x + 1] - 1;
        const different_bits = (top ^ bottom).toString(2).length;
        consumed += bits - different_bits;
        bits = different_bits;
        bottom &= 2 ** bits - 1;
        top &= 2 ** bits - 1;
        acc &= 2 ** bits - 1;
    }

    return out;
}