INADA Naoki added the comment: Digging history, duplicated code is introduced here. (1997-01-17)
https://github.com/python/cpython/commit/99304174680d4c724476dad300ae7fc638842bf0#diff-2131209d0deb0e50c93a88ec6c7b0d52 /* Optimizations based on observations by Jyrki Alakuijala (paraphrased): - This routine is very heavily used, so should be AFAP (As Fast As Possible). - Most of the time, the first try is a hit or a definite miss; so postpone the calculation of incr until we know the first try was a miss. - Write the loop twice, so we can move the test for freeslot==NULL out of the loop. - Write the loop using pointer increments and comparisons rather than using an integer loop index. Note that it behooves the compiler to calculate the values of incr*sizeof(*ep) outside the loops and use this in the increment of ep. I've reduced the number of register variables to the two most obvious candidates. At the time, there was a single lookdict function, and three tries. * The comment said the first try was for skipping `inc` calculation. While `inc` had been removed already, I think this implies skipping freeslot==NULL test. * After first try, there are two loop for skipping freeslot==NULL test until first dummy found. This optimization looks gone. As I said above, lookdict_unicode_nodummy and lookdict_split only search from table without dummies. And lookdict_unicode() and lookdict() are not so important lookmapping() was in 1997, duplicated code only for skipping one freeslot==NULL doesn't make sense. One possible optimization is removing freeslot completely. because: * freeslot is used only when inserting. finding is more important. * insertdict() can find dummy quickly, only looking dk_indices. But before trying optimization, I suggest to remove duplicated code first. Macro bench doesn't show significant difference at least. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue29304> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
