BeRoPNG - A very tiny but complete PNG loader

[BeRo]

Any ideas?

cheers,
Paul

Just remove DataSize:longword; and the DataEnd checks from BeRoPNG (change "while (pansichar(DataPtr)+11)<pansichar(DataEnd) do begin
" to "while true do begin" and so on, but without this it's a security leak then. :-)

[paul_nicholls]

Just remove DataSize:longword; and the DataEnd checks from BeRoPNG (change "while (pansichar(DataPtr)+11)<pansichar(DataEnd) do begin
" to "while true do begin" and so on, but without this it's a security leak then. :-)

Thanks I think I might just leave it then haha

cheers,
Paul

[deathshadow]

Still, you're swap32 function should be longword, not word, no?

word and $FFFF0000 === 0 -- ALWAYS
word shl 16 === 0 -- ALWAYS.

So in effect:

result:=(Swap16(x and $ffff) shl 16) or Swap16((x and $ffff0000) shr 16);

is the same thing as saying

result:=0;

Which means on big-endian systems when your swap function is called, you'll get nothing but zero.

Also, you're sending zero to your swap16 function...

function Swap32(x:longword):longword;
begin
 result:=(Swap16(x and $ffff) shl 16) or Swap16(x shr 16);
end;

Is what you should have there. What you have right now won't work... Thankfully it's only called on big endian systems -- and you've probably only tested little endian.

It may also need typecasting forced, since swap16 returns word, not longword meaning that shl 16 could STILL result in zero.

[BeRo]

word and $FFFF0000 === 0 -- ALWAYS
word shl 16 === 0 -- ALWAYS.

Sorry, you're wrong. See my code again:

function Swap32(x:word):word;
begin
 result:=(Swap16(x and $ffff) shl 16) or Swap16((x and $ffff0000) shr 16);
end;

The first swap16 call gets "x and $ffff", and the result of it will shifted 16 bits to left, which's correct.
The second swap16 call gets "(x and $ffff0000) shr 16" or short "x shr 16", and the result of it will not shifted because it was already shifted 16 bits to right, which's also correct.

I guess, you had simply overlook the correct nested levels of the (...) blocks in my code.

[deathshadow]

Forgot about this thread... but:

function Swap32(x:word):word;

word is 16 bit unsigned... can only contain 0..$FFFF -- therein:

x and $ffff returns X

x and $ffff0000 returns 0, always...

since $FFFF is the highest number WORD can contain, $0000FFFF and $FFFF0000 == 0, ALWAYS. X in your function CANNOT hold a value that would return anything but zero on that second AND.... EVER.

See what I'm saying? for that function to work X would have to be DWORD and/or Longint... 32 bit... not 16 bit which is what WORD is.

[BeRo]

See what I'm saying? for that function to work X would have to be DWORD and/or Longint... 32 bit... not 16 bit which is what WORD is.

Yeah, I know (see the rest of the code), but this is unimportant, since this is 1. just a typo error in the typedef in the functiondef paramdef header (which's quick fixable) and 2. unused on little-endian systems