Serhiy Storchaka added the comment:
Proposed patch makes the degenerate case less hard while preserves the
optimization for common case.
$ ./python -m timeit -s 's = "АБВГД"*10**5' -- 's.find("є")'
1000 loops, best of 3: 330 usec per loop
$ ./python -m timeit -s 's = "АБВГД"*10**5' -- 's.rfind("є")'
1000 loops, best of 3: 325 usec per loop
$ ./python -m timeit -s 's = "АБВГД"*10**5' -- 's.find("Є")'
100 loops, best of 3: 7.81 msec per loop
$ ./python -m timeit -s 's = "АБВГД"*10**5' -- 's.rfind("Є")'
100 loops, best of 3: 8.5 msec per loop
$ ./python -m timeit -s 's = "АБВГД"*10**5' -- 's.find("є")'
1000 loops, best of 3: 317 usec per loop
$ ./python -m timeit -s 's = "АБВГД"*10**5' -- 's.rfind("є")'
1000 loops, best of 3: 327 usec per loop
$ ./python -m timeit -s 's = "АБВГД"*10**5' -- 's.find("Є")'
1000 loops, best of 3: 1.1 msec per loop
$ ./python -m timeit -s 's = "АБВГД"*10**5' -- 's.rfind("Є")'
1000 loops, best of 3: 964 usec per loop
The slowdown is decreased from 25 times to 3 times.
The idea is that after memchr found false positive, make a tens iterations of
simple loop before calling memchr again. This splits the cost of the memchr
call with a tens of characters.
The patch also makes a little refactoring. STRINGLIB(fastsearch_memchr_1char)
now is renamed and split on two functions STRINGLIB(find_char) and
STRINGLIB(rfind_char) with simpler interface. All preconditional checks are
moved into these functions. These functions now are directly used in other
files.
----------
keywords: +patch
resolution: remind ->
stage: needs patch -> patch review
Added file: http://bugs.python.org/file41035/find_char.patch
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<http://bugs.python.org/issue24821>
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