How to use the bcrypto/lib/sha512.mac function in bcrypto

fromSeed(seed) {
    assert(Buffer.isBuffer(seed));

    if (seed.length * 8 < common.MIN_ENTROPY
        || seed.length * 8 > common.MAX_ENTROPY) {
      throw new Error('Entropy not in range.');
    }

    const hash = sha512.mac(seed, SEED_SALT);
    const left = hash.slice(0, 32);
    const right = hash.slice(32, 64);

    // Only a 1 in 2^127 chance of happening.
    if (!secp256k1.privateKeyVerify(left))
      throw new Error('Master private key is invalid.');

    this.depth = 0;
    this.parentFingerPrint = 0;
    this.childIndex = 0;
    this.chainCode = right;
    this.privateKey = left;
    this.publicKey = secp256k1.publicKeyCreate(left, true);

    return this;
  }

fromSeed(seed) {
    assert(Buffer.isBuffer(seed));

    if (seed.length * 8 < common.MIN_ENTROPY
        || seed.length * 8 > common.MAX_ENTROPY) {
      throw new Error('Entropy not in range.');
    }

    const hash = sha512.mac(seed, SEED_SALT);
    const left = hash.slice(0, 32);
    const right = hash.slice(32, 64);

    // Only a 1 in 2^127 chance of happening.
    if (!secp256k1.privateKeyVerify(left))
      throw new Error('Master private key is invalid.');

    this.depth = 0;
    this.parentFingerPrint = 0;
    this.childIndex = 0;
    this.chainCode = right;
    this.privateKey = left;
    this.publicKey = secp256k1.publicKeyCreate(left, true);

    return this;
  }

return cache;

    const bw = bio.pool(37);

    if (index & common.HARDENED) {
      bw.writeU8(0);
      bw.writeBytes(this.privateKey);
      bw.writeU32BE(index);
    } else {
      bw.writeBytes(this.publicKey);
      bw.writeU32BE(index);
    }

    const data = bw.render();

    const hash = sha512.mac(data, this.chainCode);
    const left = hash.slice(0, 32);
    const right = hash.slice(32, 64);

    let key;
    try {
      key = secp256k1.privateKeyTweakAdd(this.privateKey, left);
    } catch (e) {
      return this.derive(index + 1);
    }

    if (this.fingerPrint === -1) {
      const fp = hash160.digest(this.publicKey);
      this.fingerPrint = fp.readUInt32BE(0, true);
    }

    const child = new this.constructor();

throw new Error('Depth too high.');

    const id = this.getID(index);
    const cache = common.cache.get(id);

    if (cache)
      return cache;

    const bw = bio.pool(37);

    bw.writeBytes(this.publicKey);
    bw.writeU32BE(index);

    const data = bw.render();

    const hash = sha512.mac(data, this.chainCode);
    const left = hash.slice(0, 32);
    const right = hash.slice(32, 64);

    let key;
    try {
      key = secp256k1.publicKeyTweakAdd(this.publicKey, left, true);
    } catch (e) {
      return this.derive(index + 1);
    }

    if (this.fingerPrint === -1) {
      const fp = hash160.digest(this.publicKey);
      this.fingerPrint = fp.readUInt32BE(0, true);
    }

    const child = new this.constructor();

throw new Error('Depth too high.');

    const id = this.getID(index);
    const cache = common.cache.get(id);

    if (cache)
      return cache;

    const bw = bio.pool(37);

    bw.writeBytes(this.publicKey);
    bw.writeU32BE(index);

    const data = bw.render();

    const hash = sha512.mac(data, this.chainCode);
    const left = hash.slice(0, 32);
    const right = hash.slice(32, 64);

    let key;
    try {
      key = secp256k1.publicKeyTweakAdd(this.publicKey, left, true);
    } catch (e) {
      return this.derive(index + 1);
    }

    if (this.fingerPrint === -1) {
      const fp = hash160.digest(this.publicKey);
      this.fingerPrint = fp.readUInt32BE(0, true);
    }

    const child = new this.constructor();

return cache;

    const bw = bio.pool(37);

    if (index & common.HARDENED) {
      bw.writeU8(0);
      bw.writeBytes(this.privateKey);
      bw.writeU32BE(index);
    } else {
      bw.writeBytes(this.publicKey);
      bw.writeU32BE(index);
    }

    const data = bw.render();

    const hash = sha512.mac(data, this.chainCode);
    const left = hash.slice(0, 32);
    const right = hash.slice(32, 64);

    let key;
    try {
      key = secp256k1.privateKeyTweakAdd(this.privateKey, left);
    } catch (e) {
      return this.derive(index + 1);
    }

    if (this.fingerPrint === -1) {
      const fp = hash160.digest(this.publicKey);
      this.fingerPrint = fp.readUInt32BE(0, true);
    }

    const child = new this.constructor();