Kotlin `toInt()` Two's Complement - kotlin

Question

I believe FFFFFFFF is -1 because of Two's Complement.
I tried to convert Hex String into Integer, but I got the error.
Here is the code I have tried.
code
// Extension functions
val Int.asByteArray get() =
byteArrayOf(
(this shr 24).toByte(),
(this shr 16).toByte(),
(this shr 8).toByte(),
this.toByte())
val Int.asHex get() = this.asByteArray.asHexUpper
// Main Code
fun main()
{
println((-1).asHex)
println("FFFFFFFF".toInt(16))
}
Result
FFFFFFFF
Exception in thread "main" java.lang.NumberFormatException: For input string: "FFFFFFFF"
at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.base/java.lang.Integer.parseInt(Integer.java:652)
at java.base/java.lang.Integer.parseInt(Integer.java:770)
Is this intended? or Is this error?
If this is intended, then what should I do?

Answer 1

Your code presumably can't parse 4 bytes (32 bit) to a signed integer, since this only contains 31 bits as one bit is reserved for the sign.
A solution would be to parse it into an unsigned integer (as Some random IT boy stated) and then convert the (16bit-)UInt to a (16bit-)Int:
fun main()
{
val u = "FFFFFFFF".toUInt(16) //16 as it is base 16
println(u) //prints "4294967295"
val v = u.toInt()
println(v) //prints "-1"
}
Use with caution as this will not work when your data is not of length 32: You can not parse FFFF and expect it to be -1 as it would be parsed to 0000FFFF which is equal to 65535.
For data lengths of 1, 2 or 8 bytes, look into the data types Byte, Short or Long and their respective Functions:
val u = "FFFFFFFF".toULong(16)
println(u) //prints 4294967295
val v = u.toLong()
println(v) //still prints 4294967295

Answer 2

It's -1 because the first bit of the 4 byte memory block decides the sign of the number. In this case since it's all 1's then it's a negative number. Then the value of this memory block is the Two's complement because we're dealing with a signed integer
The problem you're facing is not Kotlin specific: checkout this question from StackOverflow
Java has also trouble parsing such string to an Integer, but a Long has no trouble; because it has 4 more bytes to spare, and in fact, if you'd write the value literal 0xFFFFFFFF Kotlin grabs it as if it's a Long:
A quick fix for these could be to use the unsigned counterpart of the int UInt
"FFFFFFFF".toUInt(16) // 4294967295
Or just use a Long
In https://kotlinlang.org/