Can I use the UInt class to make this easier to re...

# getting-started

[Stefan Oltmann]

Can I use the UInt class to make this easier to read?

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

[Raphael TEYSSANDIER]

Should make a infix + extension function

[Raphael TEYSSANDIER]

private infix fun Byte.getUInt16(byte: Byte): Int =
    toInt() shl 8 and 0xFF00 or (byte.toInt() and 0xFF)

[Klitos Kyriacou]

It's not much better than the original, but you can do:

private fun getUInt16(firstByte: Byte, secondByte: Byte): Int =
    firstByte.toUByte().toInt() shl 8 or secondByte.toUByte().toInt()

... though if your function is called getUInt16, maybe it should return a UInt instead of an Int; then the expression becomes slightly simpler:

private fun getUInt16(firstByte: Byte, secondByte: Byte): UInt =
        firstByte.toUByte() * 256u + secondByte.toUByte()

(though I've had to use arithmetic operations because Kotlin doesn't allow bitwise operations on UByte for some strange reason)

[ephemient]

as far as the JVM goes, there are no bitwise operators on bytes, only ints and longs. most native platforms are similar, and JS is worse (only int)

[Stefan Oltmann]

@Raphael TEYSSANDIER @Klitos Kyriacou @ephemient Thank you all for your advice.

I changed it to infix and do this now:

const val INT16_BYTE_SIZE: Int = 2
const val INT24_BYTE_SIZE: Int = 3
const val INT32_BYTE_SIZE: Int = 4

fun Byte.toInt8(): Byte = this

fun Byte.toUInt8(): Short = (toInt() and 0xFF).toShort()

fun ByteArray.toInt16(): Short {

    require(size == INT16_BYTE_SIZE) { "Required $INT16_BYTE_SIZE bytes, but was $size" }

    return (this[0].toShort().toInt() shl 8 and 0xFF00.toShort().toInt() or
        (this[1].toShort().toInt() and 0xFF.toShort().toInt())).toShort()
}

fun ByteArray.toUInt16(): Int {

    require(size == INT16_BYTE_SIZE) { "Required $INT16_BYTE_SIZE bytes, but was $size" }

    return this[0].toInt() shl 8 and 0xFF00 or (this[1].toInt() and 0xFF)
}

fun ByteArray.toInt24(): Int {

    require(size == INT24_BYTE_SIZE) { "Required $INT24_BYTE_SIZE bytes, but was $size" }

    return this[0].toInt() shl 16 and 0xFF0000 or
        (this[1].toInt() shl 8 and 0xFF00) or
        (this[2].toInt() and 0xFF)
}

fun ByteArray.toInt32(): Int {

    require(size == INT32_BYTE_SIZE) { "Required $INT32_BYTE_SIZE bytes, but was $size" }

    return this[0].toInt() shl 24 and -0x1000000 or
        (this[1].toInt() shl 16 and 0xFF0000) or
        (this[2].toInt() shl 8 and 0xFF00) or
        (this[3].toInt() and 0xFF)
}

fun ByteArray.toUInt32(): Long {

    require(size == INT32_BYTE_SIZE) { "Required $INT32_BYTE_SIZE bytes, but was $size" }

    return this[0].toLong() shl 24 and 0xFF000000L or
        (this[1].toLong() shl 16 and 0xFF0000L) or
        (this[2].toLong() shl 8 and 0xFF00L) or
        (this[3].toLong() and 0xFFL)
}

[Klitos Kyriacou]

Just wondering why you're doing this[0].toShort().toInt() - isn't that the same as this[0].toInt()?

[Klitos Kyriacou]

Some of these functions can be implemented using ByteBuffer.getInt() etc.

[Stefan Oltmann]

How?

[Stefan Oltmann]

Oh, yes, after converting the original Java code to Kotlin I did not test it further. But indeed... toInt16 can also be written like (this[0].toInt() shl 8 and 0xFF00 or (this[1].toInt() and 0xFF)).toShort() with the same output.

[Klitos Kyriacou]

fun ByteArray.toInt32() = ByteBuffer.wrap(this).getInt()

[Stefan Oltmann]

ByteBuffer is a JVM class, right? I should have mentioned that I'm on Kotlin/Native for Multiplatform. 🙂

[Klitos Kyriacou]

No worries. Yes it is a JVM class, so it won't work on Kotlin Native.

[ephemient]

okio.Buffer has similar functions on multiplatform

[Stefan Oltmann]

Thanks for the hint.