DataBuffers PeekByte() returns negative values

Monkey Forums/Monkey Bug Reports/DataBuffers PeekByte() returns negative values

Pharmhaus

(Posted 2014) [#1]

Hi mark,

don't know if this is a bug but this returns negative numbers:

Strict
Import brl.databuffer

Function Main:Int()

	Local db:DataBuffer = New DataBuffer(1024)
	db.PokeByte(1, 252)
	Local i:int = db.PeekByte(1)
	Print i
	Return 0
End

If this is by-design, would you consider providing a ReadUByte() Method for the databuffer?

Pharmhaus

(Posted 2014) [#2]

Sorry, I though it was already fixed but I run the wrong test case, this still exists in 81b

Danilo

(Posted 2014) [#3]

You can easily read it as unsigned data by using a 'binary And' operation to mask out the relevant bits:

Strict
Import brl.databuffer

Function Main:Int()

    Local db:DataBuffer = New DataBuffer(1024)

    Print "Byte:"
    db.PokeByte(1, 252)
    'db.PokeByte(1, -4)
    
    Print db.PeekByte(1)          ' Read  signed  Byte
    Print db.PeekByte(1) & $FF    ' Read unsigned Byte

    Print "Word/Short:"
    db.PokeShort(1, 65500)
    'db.PokeShort(1, -36)
    
    Print db.PeekShort(1)         ' Read  signed  Word
    Print db.PeekShort(1) & $FFFF ' Read unsigned Word

    Return 0
End

It is good to have both ways. Read data and interpret it as signed and unsigned data.

Pharmhaus

(Posted 2014) [#4]

Well, If you tell me this is by design, could this at least be stated in the docs that the returned value is signed (maybe in bold)?
Wouldn't have changed anything as I simply ported good ol' bmax code and I would have fallen for the same trap because all I did was copy&paste.
The bit twiddling is not a problem the behaviour was simply extremly unexpected at the very moment I ported the code.

skid	(Posted 2014) [#5]

All monkey integers are signed, there is no precedent anywhere for the use of unsigned in any of it's modules that I am aware of.

Which particular blitzmax command are you talking about ph?

Pharmhaus

(Posted 2014) [#6]

Try:

SuperStrict

Local bank:TBank = CreateBank(1024)
bank.PokeByte(1, 252)

Print bank.PeekByte( 1)

And compare it with the Monkey X version.
This would be no problem for a few lines but if you try to port whole modules over things get ugly pretty fast when multiple things now work completely different.
Debugging old code n' stuff....

skid	(Posted 2014) [#7]

I concur, docs need updating as byte is specifically signed in bmx and undefined in monkey.

marksibly

(Posted 2014) [#8]

The reason it works like this is mainly because that's the way most targets natively implement the databuffer methods - ie: it's pretty much optimal.

Adding PeekUByte etc wouldn't be too much of a hassle though - will think about it.