is there a more efficient way to convert 2 bytes to a short

Question

is there a more efficient way to convert 2 bytes to a short in kotlin i m worried this is creating a bunch of intermediary types and will be a waste ```fun ByteArray getShort byteIndex Int Short val b1 = get byteIndex and 0xFF toByte toInt val b2 = get byteIndex + 1 and 0xFF toByte toInt return b1 shl 8 or b2 toShort ``` i could keep static instances of the masks `0xFF toByte ` but i still have to create the Ints which seems like a waste

karelpeeters · Answer

Unless you ve determined that there s indeed a performance problem with this code the JVM should optimize all of this just fine

karelpeeters · Answer

In particular `0xFF toByte ` is some of the easiest stuff to constant fold away

karelpeeters · Answer

But I m not sure what to want `get byteIndex and 0xFF toByte ` to do

karelpeeters · Answer

Don t you want something like this instead ```fun ByteArray getShort byteIndex Int Short val b1 = this byteIndex toInt and 0xFF val b2 = this byteIndex + 1 toInt and 0xFF return b1 shl 8 + b2 toShort ```

bbaldino · Answer

effectively i guess yeah

bbaldino · Answer

at a glance those seem logically equivalent but maybe i m missing something

bbaldino · Answer

anyway not too picky on the specifics i ll just be doing it a lot and wanted to make sure i wasn t allocating additional type instances when it wasn t really needed i ve seen it as an issue in some measurements i m taking but not this one specifically i ll start with this and worry about it later if it ends up being an issue

bbaldino · Answer

java isn t picky about the types for shift etc so it s just ```public static short makeShort byte b1 byte b2 return short b1 lt lt 8 | b2 amp 0xFF ```

karelpeeters · Answer

You re not allocating here anyway it all compiles to primitive

bbaldino · Answer

ok great wasn t sure if there was some boxing going on

karelpeeters · Answer

The problem is that when you just do ` toInt ` the value is sign extended if you do that first and then mask `and 0xFF` you should be good

bbaldino · Answer

ok yeah i ve actually got a `Byte toPositiveInt` helper i removed it to paste in the example

bbaldino · Answer

thanks

karelpeeters · Answer

Ah well that works too of course simple smile

bbaldino · Answer

and ByteArray get index i assume compiles to byte index

bbaldino · Answer

nm just confirmed the bytecode looks like it does

karelpeeters · Answer

Yeah that s literally the `operator fun` you re calling