music-metadata/lib/musepack/sv7/BitReader.js

Music metadata parser for Node.js, supporting virtual any audio and tag format.

import * as Token from 'token-types';
export class BitReader {
    constructor(tokenizer) {
        this.pos = 0;
        this.dword = null;
        this.tokenizer = tokenizer;
    }
    /**
     *
     * @param bits 1..30 bits
     */
    async read(bits) {
        while (this.dword === null) {
            this.dword = await this.tokenizer.readToken(Token.UINT32_LE);
        }
        let out = this.dword;
        this.pos += bits;
        if (this.pos < 32) {
            out >>>= (32 - this.pos);
            return out & ((1 << bits) - 1);
        }
        this.pos -= 32;
        if (this.pos === 0) {
            this.dword = null;
            return out & ((1 << bits) - 1);
        }
        this.dword = await this.tokenizer.readToken(Token.UINT32_LE);
        if (this.pos) {
            out <<= this.pos;
            out |= this.dword >>> (32 - this.pos);
        }
        return out & ((1 << bits) - 1);
    }
    async ignore(bits) {
        if (this.pos > 0) {
            const remaining = 32 - this.pos;
            this.dword = null;
            bits -= remaining;
            this.pos = 0;
        }
        const remainder = bits % 32;
        const numOfWords = (bits - remainder) / 32;
        await this.tokenizer.ignore(numOfWords * 4);
        return this.read(remainder);
    }
}