Bitshifting for bytes is not supported in Kotlin and I try to figure out how I can translate this me...

# getting-started

[Stefan Oltmann]

Bitshifting for bytes is not supported in Kotlin and I try to figure out how I can translate this method into Kotlin code:

/**
 * Returns an unsigned 16-bit int calculated from the next two bytes of the sequence.
 *
 * @return the 16 bit int value, between 0x0000 and 0xFFFF
 */
public int getUInt16() {
        return (getByte() << 8 & 0xFF00) |
               (getByte()      & 0xFF);
}

If I add .toInt() I can use the shl function, but the result is wrong.

Is there already a standard function for this calculation?

[Klitos Kyriacou]

Why doesn't (getByte().toInt() shl 8 and 0xFF00) or (getByte().toInt() and 0xFF) work for you?

[msoulatre]

I don't know why you get wrong results, this is how I do it, and it seems to work as expected :

fun ByteArray.readShort(offset: Int = 0): Int {
    return (((this[offset+0].toInt() and 0xff) shl 8) or
            ((this[offset+1].toInt() and 0xff)))
}

I do wonder if there is a better way with standard functions.

[Klitos Kyriacou]

What is your getByte() doing? Is it, for example, reading from a ByteBuffer? If so, there's already a getShort() that does what you want.

[phldavies]

If you’re using a ByteBuffer instance (assumedly from the getByte() calls) then you can do getShort().toUShort() to get a UShort , or getShort().toInt() and 0xFFFF (or getShort().toUShort().toInt() ) to get it as an Int

[phldavies]

If you weren’t aware, Kotlin does have unsigned integer types

[Stefan Oltmann]

Thank you all a lot.

Why doesn't (getByte().toInt() shl 8 and 0xFF00) or (getByte().toInt() and 0xFF) work for you?

That works, thank you.

I used IDEA automatic Java to Kotlin conversion and overlooked a missing paranthesis. 🙈
I expected the problem somewhere else. 🙄

This is correct:

fun getUInt16(firstByte: Byte, secondByte: Byte): Int =
    firstByte.toInt() shl 8 and 0xFF00 or (secondByte.toInt() and 0xFF)

And this returns the wrong result:

fun getUInt16(firstByte: Byte, secondByte: Byte): Int =
    firstByte.toInt() shl 8 and 0xFF00 or secondByte.toInt() and 0xFF

[Chris Miller]

I filed a similar bug on this a while ago, it caused me quite a bit of head-scratching and debugging at the time: https://youtrack.jetbrains.com/issue/KTIJ-19959/Java-to-Kotlin-coversion-fails-to-take-into-account-operator-pre

[Stefan Oltmann]

Exactly that happened to me. Thank you for reporting. 🙂