decodeBinary64 = (encoded, skip = 0) => {
  encoded.charAt(skip) === 'f' || Fail`Encoded number expected: ${encoded}`;
  let bits = BigInt(`0x${getSuffix(encoded, skip + 1)}`);
  if (encoded.charAt(skip + 1) < '8') {
    bits ^= 0xffffffffffffffffn;
  } else {
    bits ^= 0x8000000000000000n;
  }
  asBits[0] = bits;
  const result = asNumber[0];
  !is(result, -0) ||
    Fail`Unexpected negative zero: ${getSuffix(encoded, skip)}`;
  return result;
}
@param {string} encoded
@param {number} [skip]
@returns {number}