diff options
Diffstat (limited to 'doc/plzip.texi')
| -rw-r--r-- | doc/plzip.texi | 63 |
1 files changed, 42 insertions, 21 deletions
diff --git a/doc/plzip.texi b/doc/plzip.texi index 413a9e3..c55e95d 100644 --- a/doc/plzip.texi +++ b/doc/plzip.texi @@ -6,8 +6,8 @@ @finalout @c %**end of header -@set UPDATED 20 January 2014 -@set VERSION 1.2-pre1 +@set UPDATED 8 May 2014 +@set VERSION 1.2-rc1 @dircategory Data Compression @direntry @@ -68,29 +68,50 @@ but on files of only a few MB plzip is no faster than lzip. Plzip uses the lzip file format; the files produced by plzip are fully compatible with lzip-1.4 or newer, and can be rescued with lziprecover. -The lzip file format is designed for long-term data archiving and -provides very safe integrity checking. The member trailer stores the -32-bit CRC of the original data, the size of the original data and the -size of the member. These values, together with the value remaining in -the range decoder and the end-of-stream marker, provide a 4 factor -integrity checking which guarantees that the decompressed version of the -data is identical to the original. This guards against corruption of the -compressed data, and against undetected bugs in plzip (hopefully very -unlikely). The chances of data corruption going undetected are -microscopic. Be aware, though, that the check occurs upon decompression, -so it can only tell you that something is wrong. It can't help you -recover the original uncompressed data. - -If you ever need to recover data from a damaged lzip file, try the -lziprecover program. Lziprecover makes lzip files resistant to bit-flip -(one of the most common forms of data corruption), and provides data -recovery capabilities, including error-checked merging of damaged copies -of a file. +The lzip file format is designed for long-term data archiving, taking +into account both data integrity and decoder availability: + +@itemize @bullet +@item +The lzip format provides very safe integrity checking and some data +recovery means. The lziprecover program can repair bit-flip errors (one +of the most common forms of data corruption) in lzip files, and provides +data recovery capabilities, including error-checked merging of damaged +copies of a file. + +@item +The lzip format is as simple as possible (but not simpler). The lzip +manual provides the code of a simple decompressor along with a detailed +explanation of how it works, so that with the only help of the lzip +manual it would be possible for a digital archaeologist to extract the +data from a lzip file long after quantum computers eventually render +LZMA obsolete. + +@item +Additionally lzip is copylefted, which guarantees that it will remain +free forever. +@end itemize + +The member trailer stores the 32-bit CRC of the original data, the size +of the original data and the size of the member. These values, together +with the value remaining in the range decoder and the end-of-stream +marker, provide a 4 factor integrity checking which guarantees that the +decompressed version of the data is identical to the original. This +guards against corruption of the compressed data, and against undetected +bugs in plzip (hopefully very unlikely). The chances of data corruption +going undetected are microscopic. Be aware, though, that the check +occurs upon decompression, so it can only tell you that something is +wrong. It can't help you recover the original uncompressed data. Plzip uses the same well-defined exit status values used by lzip and bzip2, which makes it safer than compressors returning ambiguous warning values (like gzip) when it is used as a back end for tar or zutils. +Plzip will automatically use the smallest possible dictionary size for +each file without exceeding the given limit. Keep in mind that the +decompression memory requirement is affected at compression time by the +choice of dictionary size limit. + When compressing, plzip replaces every file given in the command line with a compressed version of itself, with the name "original_name.lz". When decompressing, plzip attempts to guess the name for the decompressed @@ -238,7 +259,7 @@ Quiet operation. Suppress all messages. @itemx --dictionary-size=@var{bytes} Set the dictionary size limit in bytes. Valid values range from 4 KiB to 512 MiB. Plzip will use the smallest possible dictionary size for each -member without exceeding this limit. Note that dictionary sizes are +file without exceeding this limit. Note that dictionary sizes are quantized. If the specified size does not match one of the valid sizes, it will be rounded upwards by adding up to (@var{bytes} / 16) to it. |