ReduceByteArray.kt

private inline fun <R> ByteArray.reduce(
    offset: Int, size: Int, default: R,
    reducer: (acc: R, element: Byte, offsetIdx: Int) -> R
): R {
    var acc = default
    val upperBound = offset + size
    if (0 > offset && upperBound >= size) throw RuntimeException("Selected range not in bound. ${offset until upperBound} !in $indices")
    for (i in offset until upperBound) {
        acc = reducer(acc, get(i), i - offset)
    }
    return acc
}

fun Long.toByteArray() = ByteArray(Long.SIZE_BYTES) { ((this shr (8 * it)) and 0xFF).toByte() }
fun ByteArray.toLong(at: Int) = reduce(at, Long.SIZE_BYTES, 0L) { acc, element, offsetIdx ->
    acc or ((element.toLong() and 0xFF) shl (offsetIdx * 8))
}

inline fun Int.toByteArray() = ByteArray(Int.SIZE_BYTES) { ((this shr (8 * it)) and 0xFF).toByte() }
inline fun ByteArray.decodeInt(at: Int = 0) = reduce(at, Int.SIZE_BYTES, 0) { acc, element, offsetIdx ->
    acc or ((element.toInt() and 0xFF) shl (offsetIdx * 8))
}