BigInt 和 Bytes 互转

bigint.ts

/**
 * @module bigint
 */

function getByteLength(value: bigint): number {
  if (value === 0n || value === -1n) {
    return 1;
  }

  if (value < 0n) {
    value = ~value;
  }

  let bitLength = 0;

  while (value > 0n) {
    bitLength++;
    value >>= 1n;
  }

  return Math.ceil(bitLength / 8) + 1;
}

export function bigIntToBytes(value: bigint, littleEndian: boolean = false): Uint8Array {
  const byteLength = getByteLength(value);
  const bytes = new Uint8Array(byteLength);

  if (littleEndian) {
    for (let offset = 0; offset < byteLength; offset++) {
      const currentBitShift = offset * 8;

      bytes[offset] = Number((value >> BigInt(currentBitShift)) & 0xffn);
    }
  } else {
    const highestBitShift = (byteLength - 1) * 8;

    for (let offset = 0; offset < byteLength; offset++) {
      const currentBitShift = highestBitShift - offset * 8;

      bytes[offset] = Number((value >> BigInt(currentBitShift)) & 0xffn);
    }
  }

  return bytes;
}

export function bytesToBigInt(bytes: Uint8Array, littleEndian: boolean = false): bigint {
  let value = 0n;

  const { byteLength } = bytes;

  if (byteLength > 0) {
    const maxOffset = byteLength - 1;
    const isNegative = (bytes[littleEndian ? maxOffset : 0] & 0x80) !== 0;

    if (isNegative) {
      for (let offset = 0; offset < byteLength; offset++) {
        const byte = bytes[littleEndian ? maxOffset - offset : offset];

        value = (value << 8n) | BigInt(byte ^ 0xff);
      }

      return ~value;
    }

    for (let offset = 0; offset < byteLength; offset++) {
      const byte = bytes[littleEndian ? maxOffset - offset : offset];

      value = (value << 8n) | BigInt(byte & 0xff);
    }

    return value;
  }

  return value;
}