CRC32 checksum generation in a few lines of Swift 5. https://en.wikipedia.org/wiki/Cyclic_redundancy_check#CRC-32_algorithm

CRC32.swift

class CRC32 {
        
    static var table: [UInt32] = {
        (0...255).map { i -> UInt32 in
            (0..<8).reduce(UInt32(i), { c, _ in
                (c % 2 == 0) ? (c >> 1) : (0xEDB88320 ^ (c >> 1))
            })
        }
    }()

    static func checksum(bytes: [UInt8]) -> UInt32 {
        return ~(bytes.reduce(~UInt32(0), { crc, byte in
            (crc >> 8) ^ table[(Int(crc) ^ Int(byte)) & 0xFF]
        }))
    }
}