Kotlin bit shifting

Question

I want to convert the code if this answer to Kotlin: https://stackoverflow.com/a/5402769/2735398

I pasted this into Intellij:

private int decodeInt() {
    return ((bytes[pos++] & 0xFF) << 24) | ((bytes[pos++] & 0xFF) << 16)
            | ((bytes[pos++] & 0xFF) << 8) | (bytes[pos++] & 0xFF);
}

Intellij asks if I want to convert it to Kotlin, when I do this is the output:

private fun decodeInt(): Int {
    return (bytes[pos++] and 0xFF shl 24 or (bytes[pos++] and 0xFF shl 16)
            or (bytes[pos++] and 0xFF shl 8) or (bytes[pos++] and 0xFF))
}

At all 0xFF I get this error:

The integer literal does not conform to the expected type Byte

By appending .toByte() after it I was able to remove this error.

And at all shift left operations(shl) I get this error:

Unresolved reference. None of the following candidates is applicable because of receiver type mismatch: 

@SinceKotlin @InlineOnly public infix inline fun BigInteger.shl(n: Int): BigInteger defined in kotlin

I wasn't able to solve this one... I don't know a lot about bit shifting in Java/Kotlin...
What would be the working Kotlin code for this?

DPM · Accepted Answer · 2018-01-31T22:23:54.177

14

Convert explicitly like this: 0xFF.toByte()

As a general rule, press Alt+Enter when you need more information about an error or a possible solution.

The shift left method takes an Int as parameter. So, same thing, convert to the right type.

(bytes[pos++] and 0xFF.toByte()).toInt() shl 24

edited Jan 31 '18 at 22:23

answered Jan 31 '18 at 22:15

DPM

1,960
3
26
49

This has 8 conversions. It works, but it can be done with just 4 conversions. – Paul Hicks Feb 01 '18 at 00:45
@Paul Hicks You're probably right. I'll counter your donwvote on the basis that I don't see how your answer is any worse and the person who downvoted didn't say what's wrong with it. – DPM Feb 01 '18 at 00:59

Paul Hicks · Answer 2 · 2018-02-01T00:46:13.600

2

shl expects Int, not Byte. You need 0xFF to be an Int (which it is), so don't call toByte(). You need (0xFF shl 24) to be an Int, so don't convert that. You need bytes[pos++] to be an Int.. convert that!

return (((bytes[pos++].toInt() and (0xFF shl 24)) or
         (bytes[pos++].toInt() and (0xFF shl 16)) or
         (bytes[pos++].toInt() and (0xFF shl 8)) or
         (bytes[pos++].toInt() and 0xFF))

edited Feb 01 '18 at 00:46

answered Jan 31 '18 at 22:26

Paul Hicks

13,289
5
51
78

1

Or possibly even better.. change `bytes` to be an Int array rather than a Byte array. It will be faster in most cases, though obviously use more memory. – Paul Hicks Jan 31 '18 at 22:29

Kotlin bit shifting

2 Answers2