Declarative Kotlin SHA-512 Checksum

Checksum.kt

import java.security.MessageDigest

/**
* This code is based on https://medium.com/rayn-studios/generating-sha-512-checksum-of-a-file-in-android-42ae135b0a52
*                       https://gist.github.com/rajat1saxena/738da60a88413a8c5b0bb8f41e31e796
*                       https://gist.github.com/rajat1saxena/ddd6301fd6564954e204eed23dcce2f4
*/

class Checksum(private val data: ByteArray) {

    private val algorithm = "SHA-512"

    private fun generateChecksum(): String {
        val digest = MessageDigest.getInstance(algorithm)
        return printableHexString(digest.digest(data))
    }

    private fun printableHexString(digestedHash: ByteArray): String {
        return digestedHash.map { Integer.toHexString(0xFF and it.toInt()) }
                           .map { if (it.length < 2) "0$it" else it }
                           .fold("", { acc, d -> acc + d })
    }

    override fun toString(): String {
        return generateChecksum()
    }
}

private fun printableHexString(digestedHash: ByteArray) =
    digestedHash.asUByteArray().joinToString(separator = "") { it.toString(16).padStart(2, '0') }

or

private fun ByteArray.printableHexString() = 
    asUByteArray().joinToString(separator = "") { it.toString(16).padStart(2, '0') }