classification
Title: Use PyUnicode_MAX_CHAR_VALUE instead of PyUnicode_KIND in some API's short path
Type: enhancement Stage: resolved
Components: Interpreter Core Versions: Python 3.7
process
Status: closed Resolution: rejected
Dependencies: Superseder:
Assigned To: Nosy List: serhiy.storchaka, xiang.zhang
Priority: normal Keywords: patch

Created on 2016-12-12 11:22 by xiang.zhang, last changed 2016-12-12 12:45 by xiang.zhang. This issue is now closed.

Files
File name Uploaded Description Edit
short-path.patch xiang.zhang, 2016-12-12 11:22 review
Messages (3)
msg282982 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-12-12 11:22
Some unicode APIs like PyUnicode_Contains get a short path comparing kinds. But this get a problem cannot apply to ascii and latin1. PyUnicode_MAX_CHAR_VALUE could be used instead to make the short path also apply to ascii and latin1. This skill is already used in PyUnicode_Replace.
msg282983 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-12-12 11:37
PyUnicode_KIND() just extracts three bits from the state word. PyUnicode_MAX_CHAR_VALUE() extracts bits multiple times and does few conditional branching. I think it is much slower that PyUnicode_KIND(). In common case you search ASCII needle or the needle of the same kind as a string, therefore checking for fast path just adds the overhead. It is appropriate while the overhead is tiny.

Optimize common cases, not rare and obscure cases.
msg282990 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-12-12 12:44
I know the difference and thought the overhead should be tiny (not in a critical part). But benchmarks show it's not. :-(
History
Date User Action Args
2016-12-12 12:45:04xiang.zhangsetresolution: rejected
2016-12-12 12:44:42xiang.zhangsetstatus: open -> closed

messages: + msg282990
stage: patch review -> resolved
2016-12-12 11:37:38serhiy.storchakasetmessages: + msg282983
2016-12-12 11:22:10xiang.zhangcreate