How to get an unsigned integer from a byte array in Kotlin JVM?

Question

Kotlin 1.3 introduced unsigned integer types, but I can't seem to figure out how to get an unsigned integer from a ByteArray in Kotlin JVM.

Kotlin Native has a convenient ByteArray.getUIntAt() method, but this does not exist for Kotlin JVM.

val bytes: ByteArray = byteArrayOf(1, 1, 1, 1)
val uint: UInt // = ???

What are my options here? Is there a more elegant way than using a ByteBuffer, or bit-shifting my way out of this?

Answer 1

As mentioned in the comments there is no out of the box solution in the JVM version of Kotlin. An extension function doing the same as the Kotlin/Native function might look like this:

fun ByteArray.getUIntAt(idx: Int) =
    ((this[idx].toUInt() and 0xFFu) shl 24) or
            ((this[idx + 1].toUInt() and 0xFFu) shl 16) or
            ((this[idx + 2].toUInt() and 0xFFu) shl 8) or
            (this[idx + 3].toUInt() and 0xFFu)

fun main(args: Array<String>) {

    // 16843009
    println(byteArrayOf(1, 1, 1, 1).getUIntAt(0))

    // 4294967295, which is UInt.MAX_VALUE
    println(byteArrayOf(-1, -1, -1, -1).getUIntAt(0))
}