varintiterator.kt

class VarIntIterator(
    private val bytes: ByteArray,
    private val bitsPerEntry: Int = 7,
    private val maxGroups: Int = 5,
) : Iterator<Int> {
    private var index: Int = 0

    override fun hasNext(): Boolean = index < bytes.size

    override fun next(): Int {
        if (!hasNext())
            throw NoSuchElementException("No more elements to read")

        var value = 0
        var bitsRead = 0

        val groupMask = (1 shl bitsPerEntry) - 1
        val continuationBit = 1 shl bitsPerEntry

        var b: Byte
        do {
            if (index >= bytes.size)
                throw NoSuchElementException("Unexpected end of byte array while reading VarInt")

            b = bytes[index++]
            value = value or ((b.toInt() and groupMask) shl bitsRead)
            bitsRead += bitsPerEntry

            require(bitsRead <= bitsPerEntry * maxGroups) { "VarInt size cannot exceed $maxGroups bytes" }
        } while ((b.toInt() and continuationBit) != 0)

        return value
    }
}