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]
        }))
    }
}

Thanks for this! I used checksum<T: DataProtocol>(bytes: T) to accept Data as well as [UInt8]

I have a personal vendetta against the ternary operator. Here's a simplification. ((0xEDB88320 * (c % 2)) ^ (c >> 1))

Hej hej. Thanks a lot for providing this useful code snippet! 🙏

Bug: Int(crc) should be UInt(crc)

crc is a UInt32 and on 32bit platforms Int means Int32. When the leading bit of crc is set to 1, the number cannot be represented as Int and the process will crash:

Swift/Integers.swift:3269: Fatal error: Not enough bits to represent the passed value

Feel free to take a look at this solution to prevent the crash.

License Information: Missing

While I'm here, do you mind adding a quick license note to clarify how this snippet may be reused? Without an explicit license, the default is "all rights reserved," which makes it legally awkward for others to drop it into their own projects — even with attribution.

If you're happy for people to use it freely, a one-line header like // SPDX-License-Identifier: MIT (or your preference) would settle it. No worries either way — I just wanted to check before relying on it.

Feel free to steal the snippet and use it as you want. ;)

I just translated the example from the Wikipedia page to Swift and refactored it to a more functional style.