Function truncateToBitLength

lib/internal/crypto/util.js:570–591

* Copies `bytes` up to the byte length needed for `length` bits, then clears * unused least-significant bits in the final byte. * @param {number} length * @param {ArrayBuffer|ArrayBufferView} bytes * @returns {Uint8Array}

(length, bytes)

 * @returns {Uint8Array}
 */
function truncateToBitLength(length, bytes) {
  const lengthBytes = numBitsToBytes(length);
  const isView = ArrayBufferIsView(bytes);
  const byteView = isView ?
    new Uint8Array(
      getDataViewOrTypedArrayBuffer(bytes),
      getDataViewOrTypedArrayByteOffset(bytes),
      getDataViewOrTypedArrayByteLength(bytes),
    ) :
    new Uint8Array(bytes, 0, ArrayBufferPrototypeGetByteLength(bytes));
  const result = TypedArrayPrototypeSlice(
    byteView,
    0,
    lengthBytes,
  );

  const remainder = length % 8;
  if (remainder !== 0)
    result[lengthBytes - 1] &= (0xff << (8 - remainder)) & 0xff;

  return result;
}

let webidl;