Faster *_find_max_char

[serhiy-storchaka]

BPO	15145
Nosy	@pitrou, @vstinner, @serhiy-storchaka
Files	find_max_char_2.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2012-10-17.13:56:30.972>
created_at = <Date 2012-06-22.20:51:57.901>
labels = ['interpreter-core', 'performance']
title = 'Faster *_find_max_char'
updated_at = <Date 2012-10-17.13:57:54.273>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2012-10-17.13:57:54.273>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2012-10-17.13:56:30.972>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2012-06-22.20:51:57.901>
creator = 'serhiy.storchaka'
dependencies = []
files = ['27602']
hgrepos = []
issue_num = 15145
keywords = ['patch']
message_count = 5.0
messages = ['163480', '163489', '163498', '173176', '173177']
nosy_count = 3.0
nosy_names = ['pitrou', 'vstinner', 'serhiy.storchaka']
pr_nums = []
priority = 'low'
resolution = 'rejected'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue15145'
versions = ['Python 3.4']

[serhiy-storchaka]

Here is patch that speed up *_find_max_char stringlib functions.

Microbenchmarks:

./python -m timeit -s "s='A'*20+'\x80'" "s[:-1]"
./python -m timeit -s "s='A'*20+'\U00010000'" "s[:-1]"

Results on Intel Atom N570 @ 1.66GHz:

vanilla patched

0.819 0.73
0.788 0.755

[pitrou]

0.819 0.73
0.788 0.755

Are there any circumstances where this produces a larger speedup?
I don't think a 10% improvement on a micro-benchmark is interesting at all (it's basically 0% on any real-world program).

[serhiy-storchaka]

Are there any circumstances where this produces a larger speedup?

I don't know. *_find_max_char in any case only a part of expensive
functions. Even if it is optimized to zero time, this will most likely
not produce a larger speedup.

I don't think a 10% improvement on a micro-benchmark is interesting at all (it's basically 0% on any real-world program).

I agree. It is rather a question of purity. In my opinion the function
has become easier (for developer and for compiler).

[serhiy-storchaka]

Patch updated to tip.

But because results are contradictory and often patched version even slower vanilla (and I don't understand why it happens), I close the issue. I think all changes are irrelevant and differences are only compiler optimization artifacts.

[pitrou]

Thanks for the effort, Serhiy!