[−][src]Module hash_roll::gzip
gzip (forks) rsyncable mode that uses a simple window accumulator
WARNING: not validated against gzip or rsyncrypto algorithms. Output may change to fix bugs
A widely distributed patch for gzip adds a --rsyncable flag which causes gzip to split it's
input on "stable" boundaries. This module impliments the algorithm used in that patch.
The same algorithm is used by the rsyncrypto project.
- No maximum block size is provided.
- No minimum block size is provided.
PDF of block sizes: ???
Note that the defacto-standard parameters allow a slightly more efficient check for a block split (by replacing a modulus with a bitwise-and). This impl currently doesn't allow that optimization even if you provide appropriate parameters (we need type-level integers for that).
Parameters:
- window-len: The maximum number of bytes to be examined when deciding to split a block. set to 8192 by default in gzip-rsyncable & rsyncrypto)
- modulus: set to half of window-len (so, 4096) in gzip-rsyncable & rsyncrypto.
In-block state:
- window of window-len bytes (use of the iterator interface means we also track more bytes than this)
- sum (u64)
Between-block state:
- none
References:
- http://rsyncrypto.lingnu.com/index.php/Algorithm
- https://www.samba.org/~tridge/phd_thesis.pdf
S(n) = sum(c_i, var=i, top=n, bottom=n-8196)
A(n) = S(n) / 8192
H(n) = S(n) mod 4096
Trigger splits when H(n) == 0
Structs
| GzipRsyncable | Parameters for defining the gzip rsyncable algorithm |
| GzipRsyncableIncr | Provides an incremental interface to |
| GzipRsyncableSearchState | Intermediate state for [ |