(unknown charset) [BLACKBOX] ZLib for BlackBox? Yes

From: (unknown charset) Oleg N. Cher <"Oleg>
Date: Mon, 27 Oct 2008 11:08:49 +0200

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Dear BlackBox Community,

Russian programmer Vladimir Sidorov has found and fix
two critical errors in current (and, how do I known, single)
ZLib realization in Oberon language, by Stefan Walthert.

Too, Vladimir Sidorov is author of BlackBox port of ZLib.
Thank you very much for your work, Vladimir!

1. Error in ZlibInflate.InflateCodes:

| CodeStart: (* try fast inflation while enough space available *)
IF (wavail >= 258) & (s.in.avail >= 10) THEN
InflateFast(s, wavail);
IF s.res.code # ZC.Ok THEN
IF s.res.code = ZC.StreamEnd THEN s.decode.state := CodeWash
ELSE s.decode.state := CodeBad
END
END;
EXIT
END;
s.decode.tree := s.decode.lltree;
s.decode.state := CodeLen

Must be fixed so:

| CodeStart: (* try fast inflation while enough space available *)
IF (wavail >= 258) & (s.in.avail >= 10) THEN
InflateFast(s, wavail);
IF s.res.code # ZC.Ok THEN
IF s.res.code = ZC.StreamEnd THEN s.decode.state := CodeWash
ELSE s.decode.state := CodeBad; EXIT
END
END
END;
IF s.decode.state # CodeWash THEN
s.decode.tree := s.decode.lltree;
s.decode.state := CodeLen
END

(This error is critical on data >32768 bytes)

2. Another error in ZlibInflate.NeedOut:

PROCEDURE NeedOut (VAR s: Stream; VAR wavail: INTEGER): BOOLEAN;
BEGIN
IF wavail = 0 THEN
IF (s.write = WindowSize) & (s.read # 0) THEN
s.write := 0; wavail := s.read - 1
END;
IF wavail = 0 THEN
Flush(s);
IF (s.write = WindowSize) & (s.read # 0) THEN
s.write := 0; wavail := s.read - 1
END;
IF wavail = 0 THEN
RETURN FALSE
END
END
END;
RETURN TRUE
END NeedOut;

Must be fixed so:

PROCEDURE NeedOut (VAR s: Stream; VAR wavail: INTEGER): BOOLEAN;
BEGIN
IF wavail = 0 THEN
IF (s.write = WindowSize) & (s.read # 0) THEN
s.write := 0; wavail := s.read - 1
END;
IF wavail = 0 THEN
Flush(s);
IF s.write < s.read THEN wavail := s.read - s.write - 1
ELSE wavail := WindowSize - s.write
END;
IF (s.write = WindowSize) & (s.read # 0) THEN
s.write := 0; wavail := s.read - 1
END;
IF wavail = 0 THEN
RETURN FALSE
END
END
END;
RETURN TRUE
END NeedOut;

(This error is too critical on data >32768 bytes)

This errors are present in Bluebottle (A2) too. Please, post
this information to Bluebottle developers.

Fixed version of ZLib was sent to Helmut Zinn for publishing
on his website http://www.zinnamturm.eu

--
Oleg N. Cher.
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Received on Mon Oct 27 2008 - 10:08:49 UTC