How to correctly handle Byte values greater than 127 in Kotlin?

Imagine I have a Kotlin program with a variable `b` of type `Byte`, into which an external system writes values greater than `127`. "External" means that I cannot change the type of the value it returns.

```val a:Int = 128
val b:Byte = a.toByte()```

Both `a.toByte()` and `b.toInt()` return `-128`.

Imagine I want to get the correct value (`128`) from the variable `b`. How can I do it?

In other words: What implementation of `magicallyExtractRightValue` would make the following test run?

@Test
fun testByteConversion() {
val a:Int = 128
val b:Byte = a.toByte()

System.out.println(a.toByte())
System.out.println(b.toInt())

val c:Int = magicallyExtractRightValue(b)

Assertions.assertThat©.isEqualTo(128)
}

private fun magicallyExtractRightValue(b: Byte): Int {
throw UnsupportedOperationException("not implemented")
}

**Update 1:** This solution suggested by [Thilo](

[To see links please register here]

) seems to work.

private fun magicallyExtractRightValue(o: Byte): Int = when {
(o.toInt() < 0) -> 255 + o.toInt() + 1
else -> o.toInt()
}

Good old `printf` does what we want:

java.lang.String.format("%02x", byte)

With Kotlin 1.3+ you can use [unsigned types][1]. e.g. [`toUByte`][2] ([Kotlin Playground][3]):

private fun magicallyExtractRightValue(b: Byte): Int {
return b.toUByte().toInt()
}

or even require using `UByte` directly instead of `Byte` ([Kotlin Playground][4]):

private fun magicallyExtractRightValue(b: UByte): Int {
return b.toInt()
}

For releases prior to Kotlin 1.3, I recommend creating an [extension function][5] to do this using [`and`][6]:

fun Byte.toPositiveInt() = toInt() and 0xFF

Example usage:

val a: List<Int> = listOf(0, 1, 63, 127, 128, 244, 255)
println("from ints: $a")
val b: List<Byte> = a.map(Int::toByte)
println("to bytes: $b")
val c: List<Int> = b.map(Byte::toPositiveInt)
println("to positive ints: $c")

Example output:

<!-- language: none -->

from ints: [0, 1, 63, 127, 128, 244, 255]
to bytes: [0, 1, 63, 127, -128, -12, -1]
to positive ints: [0, 1, 63, 127, 128, 244, 255]


[1]:

[To see links please register here]

[2]:

[To see links please register here]

[3]:

[To see links please register here]

[4]:

[To see links please register here]

[5]:

[To see links please register here]

[6]:

[To see links please register here]