[Python-Dev] memcmp performance

[Stefan Behnel]

Richard Saunders, 25.10.2011 01:17:
> -On [20111024 09:22], Stefan Behnel wrote:
>   >>I agree. Given that the analysis shows that the libc memcmp() is
>   >>particularly fast on many Linux systems, it should be up to the Python
>   >>package maintainers for these systems to set that option externally through
>   >>the optimisation CFLAGS.
>
> Indeed, this is how I constructed my Python 3.3 and Python 2.7 :
> setenv CFLAGS '-fno-builtin-memcmp'
> just before I configured.
>
> I would like to revisit changing unicode_compare: adding a
> special arm for using memcmp when the "unicode kinds" are the
> same will only work in two specific instances:
>
> (1) the strings are the same kind, the char size is 1
> * We could add THIS to unicode_compare, but it seems extremely
> specialized by itself

But also extremely likely to happen. This means that the strings are pure 
ASCII, which is highly likely and one of the main reasons why the unicode 
string layout was rewritten for CPython 3.3. It allows CPython to save a 
lot of memory (thus clearly proving how likely this case is!), and it would 
also allow it to do faster comparisons for these strings.

Stefan