Function parseSignedInt

yarn-project/stdlib/src/abi/utils.ts:114–135

(b: Buffer, width?: number)

 * @returns - a deserialized bigint
 */
export function parseSignedInt(b: Buffer, width?: number) {
  const buf = Buffer.from(b);

  // We get the last (width / 8) bytes where width = bits of type (i64, i32 etc)
  const slicedBuf = width !== undefined ? buf.subarray(-(width / 8)) : buf;

  // Then manually deserialize with 2's complement, with the process as follows:

  // If our most significant bit is high...
  if (0x80 & slicedBuf.subarray(0, 1).readUInt8()) {
    // We flip the bits
    for (let i = 0; i < slicedBuf.length; i++) {
      slicedBuf[i] = ~slicedBuf[i];
    }

    // Add one, then negate it
    return -(BigInt(`0x${slicedBuf.toString('hex')}`) + 1n);
  }

  // ...otherwise we just return our positive int
  return BigInt(`0x${slicedBuf.toString('hex')}`);
}