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| TestMan |
 Posted: Mon Sep 18, 2006 1:58 pm |
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Guest
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Hi all,
I've found in a file the sequence 78 9c ec bd that is starting a
compressed stream.
Any idea what could be the compression behing this magic number ?
FYI this is on illustrator 12 file format (AI).
The first char is a 'x' (7 and is maybe not part of the magic number,
but the rest of it is definitly such a number.
Rgs,
TM |
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| Carsten Neubauer |
| Posted: Mon Sep 18, 2006 3:20 pm |
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| TestMan |
| Posted: Tue Sep 19, 2006 4:30 pm |
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Carsten Neubauer a écrit :
[quote:3f83c2a808]TestMan schrieb:
...
I've found in a file the sequence 78 9c ec bd that is starting a
compressed stream.
...
Seems you ran into a ZLIB-stream.
See
ZLIB Compressed Data Format Specification version 3.3
http://www.faqs.org/rfcs/rfc1950.html
[/quote:3f83c2a808]
Viele danke Carsten,
Can you clarify how you came to that conclusion ?
I've seen no magic number in the ZLIB spec :(
Rgs,
TM |
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| Carsten Neubauer |
| Posted: Tue Sep 19, 2006 8:18 pm |
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TestMan schrieb:
[quote:9e65c8c38c]Carsten Neubauer a écrit :
TestMan schrieb:
...
I've found in a file the sequence 78 9c ec bd that is starting a
compressed stream.
...
Seems you ran into a ZLIB-stream.
See
ZLIB Compressed Data Format Specification version 3.3
http://www.faqs.org/rfcs/rfc1950.html
Viele danke Carsten,
Can you clarify how you came to that conclusion ?
I've seen no magic number in the ZLIB spec :(
Rgs,
TM
[/quote:9e65c8c38c]
There is no magic number, but 0x789C looks like a ZLIB header to me.
See section 2.2 in rfc1950.
CMF: 0x78
bits 0 to 3: compression method 8 = deflate
bits 4 to 7: window size 32kB
FLG: 0x9C
bits 0 to 4: check bits, 0x789C = 30876, which is a multiple of 31
bit 5: no preset dictionary
bits 6 to 7: compression level 2, irrelevant for decompression
0xEC and 0xBD: start of data, see rfc 1951 or use ZLIB to decode.
A 32kB window and no dictionary are standard values for ZLIB.
Compression method 8 is the only one allowed.
The check bits make it a value, dividable by 31.
So everything looks fine.
You will find those streams in a lot of files, like PDFs etc.
Regards and bon nuit,
Carsten Neubauer
http://www.c14sw.de/ |
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| Mark Adler |
| Posted: Tue Sep 19, 2006 10:38 pm |
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TestMan wrote:
[quote:60b6d815a0]Can you clarify how you came to that conclusion ?
I've seen no magic number in the ZLIB spec 
[/quote:60b6d815a0]
He's right. It's almost certainly a zlib stream. There is a set of
magic numbers that a zlib stream starts with, and 78 9c is among them.
Also the next two bytes are the beginning of a valid deflate stream.
mark |
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| TestMan |
| Posted: Wed Sep 20, 2006 5:57 am |
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Carsten Neubauer a écrit :
[quote:db9abcbf99]TestMan schrieb:
Carsten Neubauer a écrit :
TestMan schrieb:
...
I've found in a file the sequence 78 9c ec bd that is starting a
compressed stream.
...
Seems you ran into a ZLIB-stream.
See
ZLIB Compressed Data Format Specification version 3.3
http://www.faqs.org/rfcs/rfc1950.html
Viele danke Carsten,
Can you clarify how you came to that conclusion ?
I've seen no magic number in the ZLIB spec :(
Rgs,
TM
There is no magic number, but 0x789C looks like a ZLIB header to me.
See section 2.2 in rfc1950.
CMF: 0x78
bits 0 to 3: compression method 8 = deflate
bits 4 to 7: window size 32kB
FLG: 0x9C
bits 0 to 4: check bits, 0x789C = 30876, which is a multiple of 31
bit 5: no preset dictionary
bits 6 to 7: compression level 2, irrelevant for decompression
0xEC and 0xBD: start of data, see rfc 1951 or use ZLIB to decode.
A 32kB window and no dictionary are standard values for ZLIB.
Compression method 8 is the only one allowed.
The check bits make it a value, dividable by 31.
So everything looks fine.
You will find those streams in a lot of files, like PDFs etc.
Regards and bon nuit,
Carsten Neubauer
http://www.c14sw.de/
[/quote:db9abcbf99]
Crystal clear answer ! Great thanks again.
Tschüß,
TM |
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| TestMan |
| Posted: Wed Sep 20, 2006 6:00 am |
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Mark Adler a écrit :
[quote:9ee0d7ad36]TestMan wrote:
Can you clarify how you came to that conclusion ?
I've seen no magic number in the ZLIB spec :(
He's right. It's almost certainly a zlib stream. There is a set of
magic numbers that a zlib stream starts with, and 78 9c is among them.
Also the next two bytes are the beginning of a valid deflate stream.
mark
[/quote:9ee0d7ad36]
Thanks mark for the answer !
FYI this stream is part of AdobeIlustrator CS2 (AI 12) new file format
.... trying to recover a crashed AI file :(
Rgs,
TM |
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