9 Mar
2011
9 Mar
'11
4:50 p.m.
OTOH I keep all of my images compressed, precisely
because I want to know if any copy has been corrupted.
Specifically I prefer bzip2 (even though a lot of my imaging
activities from the 1990's, before I knew about bzip2, are squirreled
away in zip files and I have not necessarily moved them to bzip2).
If for some reason the only copy of a bz2 file
became partially corrupted I could know which parts were good and which parts were bad:
RECOVERING DATA FROM DAMAGED FILES
bzip2 compresses files in blocks, usually 900kbytes long.
Each block is handled independently. If a media or transmission error
causes a multi-block .bz2 file to become damaged, it may be possible to
recover data from the undamaged blocks in the file.
The compressed representation of each block is delimited by a 48-bit
pattern, which makes it possible to find the block boundaries
with reasonable certainty. Each block also carries its own 32-bit CRC, so
damaged blocks can be distinguished from undamaged ones.
bzip2recover is a simple program whose purpose is to search for blocks
in .bz2 files, and write each block out into its own .bz2
file. You can then use bzip2 -t to test the integrity of the
resulting files, and decompress those which are undamaged.
9 Mar
9 Mar
11:16 p.m.
Shoppa, Tim wrote:
OTOH I keep all
of my images compressed, precisely because I want to know if any copy has been corrupted.
Specifically I prefer bzip2 (even though a lot of my imaging
activities from the 1990's, before I knew about bzip2, are squirreled
away in zip files and I have not necessarily moved them to bzip2).
If for some reason the only copy of a bz2 file
became partially corrupted I could know which parts were good and which parts were bad:
RECOVERING DATA FROM DAMAGED FILES
bzip2 compresses files in blocks, usually 900kbytes long.
Each block is handled independently. If a media or transmission error
causes a multi-block .bz2 file to become damaged, it may be possible to
recover data from the undamaged blocks in the file.
The compressed representation of each block is delimited by a 48-bit
pattern, which makes it possible to find the block boundaries
with reasonable certainty. Each block also carries its own 32-bit CRC, so
damaged blocks can be distinguished from undamaged ones.
bzip2recover is a simple program whose purpose is to search for blocks
in .bz2 files, and write each block out into its own .bz2
file. You can then use bzip2 -t to test the integrity of the
resulting files, and decompress those which are undamaged.
10 Mar
10 Mar
5:05 a.m.
It was thus said that the Great Jerome H. Fine once stated:
Is it possible to find the md5 algorithm? I would like to run the code
under the E11 emulator to check files copied from the PC to determine if
they are still OK? I have found a number of web sites which discuss md5,
but none that have the actual algorithm.
Hope you have a C compiler, because a reference implementation of MD5 in C
can be found in RFC-1321 (http://www.ietf.org/rfc/rfc1321.txt).
-spc (It's not the best C code, but it does work)
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participants (3)
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jhfinedp3k＠compsys.to -
sean＠conman.org -
tshoppa＠wmata.com