[issue30476] Add _GenerateCRCTable() to zipfile.py to pre-compute CRC Table

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

After some investigations this idea no longer looks good to me.

The table of 256 32-bit integers will take at least 44 lines. This is too 
large. It is easier to check the algorithm than all these numbers. The error 
even in one digit can break all, but for testing we should check every element 
of the table. In any case we would need a generating code, either for 
generating the sources, or for testing.

Current generating code is 25% faster than the code used in 2.7, and 
(surprisingly!) Python 3.7 is 50% faster than Python 2.7 in the computation of 
the same code. On my computer the generating takes 1 ms (the startup time of 
the interpreter is 50 ms), and the table is generated only if ZIP file 
decryption is used, and only once.

--
resolution: not a bug -> rejected

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30476] Add _GenerateCRCTable() to zipfile.py to pre-compute CRC Table

[Martin Panter]

Changes by Martin Panter :


--
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30476] Add _GenerateCRCTable() to zipfile.py to pre-compute CRC Table

[Shubha Ramani]

Shubha Ramani added the comment:

This is not needed after all jkloth explained. Please feel free to close.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30476] Add _GenerateCRCTable() to zipfile.py to pre-compute CRC Table

[Jeremy Kloth]

Jeremy Kloth added the comment:

See bpo-10030 (and pr #550).  It removed that function in favor of the current 
approach.

Also, that current code does not generate *every* time, but just once.  Note 
that the computed value is stored in a global cache.

--
nosy: +jkloth

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30476] Add _GenerateCRCTable() to zipfile.py to pre-compute CRC Table

[Shubha Ramani]

Shubha Ramani added the comment:

It looks like _GenerateCRCTable() is already implemented here:

https://svn.python.org/projects/python/trunk/Lib/zipfile.py

The question is, why isn't it implemented here ?

https://github.com/python/cpython/blob/master/Lib/zipfile.py

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30476] Add _GenerateCRCTable() to zipfile.py to pre-compute CRC Table

[Shubha Ramani]

New submission from Shubha Ramani:

It is wasteful to generate the CRC Table every time, via _crctable = 
list(map(_gen_crc, range(256))). Better to have a pre-computed table.

I will submit the patch which incorporates this feature along with 
micro-benchmark results. Related issue:

http://bugs.python.org/issue30467

http://bugs.python.org/issue30468

--
messages: 294513
nosy: serhiy.storchaka, shubhar
priority: normal
severity: normal
status: open
title: Add   _GenerateCRCTable() to zipfile.py to pre-compute CRC Table
type: performance
versions: Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com