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Adjust the DOH string hash function

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The one we're currently using only considers the last five characters
plus the least significant bit of the last-but-sixth character, which
unsurprisingly generates a lot of many-way collisions.

This change seems to give about a 4% reduction in wallclock time for
processing li_std_list_wrap.i from the testsuite for Python.  The
hash collision rate for this example drops from 39% to 0!

Closes #2303
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Olly Betts 2022-07-07 11:50:00 +12:00
commit eaaf893605
2 changed files with 25 additions and 6 deletions
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@ -7,6 +7,17 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
Version 4.1.0 (in progress)
===========================
2022-09-29: olly
#2303 SWIG's internal hash tables now use a better hash function.
The old hash function only considerd the last five characters
plus the least significant bit of the last-but-sixth character,
which as you might guess generated a lot of many-way collisions.
This change seems to give about a 4% reduction in wallclock time
for processing li_std_list_wrap.i from the testsuite for Python.
The hash collision rate for this example drops from 39% to 0!
2022-09-29: wsfulton
#2303 Type tables are now output in a fixed order whereas previously
the order may change with any minor input code change. This shouldn't