Is `x and 0xFF.toByte()` a noop? Aka `x and 0xFF.toByte() == x` is always true?

# getting-started

[reactormonk]

Is x and 0xFF.toByte() a noop? Aka x and 0xFF.toByte() == x is always true?

[Joffrey]

What type is x?

[reactormonk]

Also Byte

[Joffrey]

Then I indeed don't quite get the point of this 🤔 Should be a noop IMO. But I'm not well versed in Kotlin's bitwise operators

[Joffrey]

If this code is old, it might come from the days when Kotlin didn't have bitwise operators on Bytes and you had to convert to Int to do this 🤷

[reactormonk]

I pasta'd it from Java code, where it was on `Int`s

[Joffrey]

Ah, then forget about my last point

[Sam]

Can you share the Java code? Typically & 0xFF would be used to truncate the sign bits or other unwanted extras. Translating it to Kotlin probably requires some understanding of the intended behaviour.

[Sam]

And Kotlin has unsigned types which might or might not make your life easier

[reactormonk]

https://github.com/skjolber/external-nfc-api/blob/master/core/src/main/java/com/github/skjolber/nfc/command/ACR1255BluetoothCommands.java#L157=

[Joffrey]

response.getData()[0] is already a byte, though. I'm not sure what the Java code wanted to do initially with this

[Sam]

I imagine the intention is to print the byte as if it is an unsigned value.

[Joffrey]

but I fail to see what difference it makes to & 0xFF (even in terms of sign bits) if the original value is a byte

[Sam]

0xFF in Java is an int, because it is too big to be a signed byte

[Sam]

Consider this Java code:

byte signed = -1;
System.out.println("Signed value is " + signed);
// Signed value is -1
int unsigned = 0xFF & signed;
System.out.println("Unsigned value is " + unsigned);
// Unsigned value is 255

[Joffrey]

Got it, I missed that & 0xFF also converts the original value to int before truncating the bits

[Sam]

As for the Kotlin equivalent:

val data: Byte = -1
println("Signed value is " + data)
println("Unsigned value is " + data.toUByte())

[Sam]

(or data.toUByte().toInt() if you want to match the Java version more exactly)