Random MAVs

BlitzMax Forums/BlitzMax Programming/Random MAVs

Jake L.

(Posted 2008) [#1]

Hi,

I tried the base64 encoder from the code archives ( http://www.blitzmax.com/codearcs/codearcs.php?code=1724 ), and it throws random errors. But I can't find any error in the code. More details in the archives entry.

Today I got another random bug when calling EndGraphics and the debugger pointed me to a line in glgraphics mod that does nothing big (setting an integer, so there can't go anything wrong). Maybe this is a 1.28 problem, I never got weird errors like this before.

Even if I run in debugmode from within the IDE all I get is an unnamed "Memory access violation", no more details :(

Anyone else getting such weird random errors?

Jake

N	(Posted 2008) [#2]

This means you're passing an incorrect buffer size or that you're just not passing a buffer, but some random memory location that does not correspond to what you're trying to encode. Check to make sure you're passing correct data and the correct size to the encoder.

Jake L.

(Posted 2008) [#3]

I thought the same until I wrote a little test app. I can't see anything wrong with this:

Const etable$ = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
Global dtable@[256]
For Local __di:Int = 0 To etable.Length-1
    dtable[etable[__di]] = __di
Next

for local i%=0 to 20000
	print "try to encode, run #"+i
	TryEncode()
Next
end

function TryEncode()
	local buf:Byte[]=New Byte[4096]
	local s$=EncodeBase64 (buf,sizeof(buf))		

end function

Function EncodeBase64$( in@ Ptr, sizein:Int )
    If sizein <= 0 Then Return Null
    Local out:Byte[64]
    Local s$
    
    Local p@ Ptr = out
    Local cc% = 0
    
    For Local i% = 0 To sizein-1 Step 3
        Local c1@, c2@
        c1 = in[i]&$FF
        c2 = in[i+1]&$FF
        
        p[0] = etable[in[0] Shr 2]
        If i+1 < sizein Then
            p[1] = etable[((in[0] & $3) Shl 4) | ((in[1] & $F0) Shr 4)]
            If i+2 < sizein Then
                p[2] = etable[((in[1] & $F) Shl 2) | ((in[2] & $C0) Shr 6)]
                p[3] = etable[in[2] & $3F]
            ElseIf i+1 < sizein Then
                p[2] = etable[((in[1] & $F) Shl 2)]
            EndIf
        Else
            p[1] = etable[((in[0] & $3) Shl 4)]
        EndIf
        
        in :+ 3
        p :+ 4
        cc :+ 4
        If cc = 64 Then
            s :+ String.FromBytes(out,cc)
            p = out
            cc = 0
        EndIf
    Next
    Select sizein Mod 3
        Case 0
            s :+ String.FromBytes(out, cc)
        Case 1
            s :+ String.FromBytes(out, cc-2)+"=="
        Case 2
            s :+ String.FromBytes(out, cc-1)+"="
    End Select
    Return s
End Function

' Assumes you're passing a valid string to it
Function DecodeBase64:Byte[]( in$ )
    Local f% = in.Find("=")
    in = in.Replace("=","~0")
    Local rm% = 0
    If f = -1 Then
        rm = 0
        f = in.Length-1
    ElseIf f = in.Length-1 Then
        rm = 1
    ElseIf f = in.Length-2 Then
        rm = 2
    EndIf
    Local out@...]
    Local p@ Ptr = out
    Local bc% = 0
    For Local cc:Int = 0 To f Step 4
        p[0] = (dtable[in[cc]] Shl 2) | (dtable[in[cc+1]] Shr 4)
        If out.Length > (bc+1) Then p[1] = ((dtable[in[cc+1]] & $F) Shl 4) | ((dtable[in[cc+2]]&$3C) Shr 2)
        If out.Length > (bc+2) Then p[2] = ((dtable[in[cc+2]] & $3) Shl 6) | dtable[in[cc+3]]
        bc :+ 3
        p :+ 3
    Next
    Return out
End Function

N	(Posted 2008) [#4]

Actually, looking over the code again, that's absolutely horrible what I wrote. I guess that's another lesson to not do things at 3am. I'll see about rewriting this. My fault here.

Jake L.

(Posted 2008) [#5]

Right in time Brucey did it again and made a Base64 class. Horray!

Brucey

(Posted 2008) [#6]

Does it work okay?

I only gave it some limited testing.

Jake L.

(Posted 2008) [#7]

Works like a charm, as all your modules do!

N	(Posted 2008) [#8]

Nice, the less work I have to do, the better.