[issue16281] TODO in tailmatch(): it does not support backward in all cases

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

The result does not depend on the direction of comparison. This only affects speed. But who can to say in which direction comparison will be faster?

Here I see a one obvious opportunity for optimization:

    if (kind_self < kind_sub)
        return 0;

After that and after processing the case (kind_self == kind_sub) only 3 special cases left: UCS1 in UCS2, UCS1 in UCS4, and UCS2 in UCS4.  Get rid of slow PyUnicode_READ() for this cases will speed up the code.  Also note that comparing first and last characters before memcmp can be a slowdown (because PyUnicode_READ() is slow).  Try to compare first and last bytes.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16281>
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