Sets of Unicode keys are picky about the primes used when generating
a perfect hash function for them. Callers can spend many seconds
iterating through all the possible combinations of candidate
multipliers and seeds to find one that works.
Unicode updates typically happen only once a year, but it still makes
development and testing of Unicode scripts unnecessarily slow. To fix,
iterate over the primes in the innermost loop. This does not change
any existing functions checked into the tree.
80f8eb7 has added to the normalization quick check headers some code
generated by PerfectHash.pm that is incompatible with the settings of
gitattributes for this repository, as whitespaces followed a set of tabs
for the first element of a line in the table. Instead of adding a new
exception to gitattributes, rework the format generated so as a right
padding with spaces is used instead of a left padding. This keeps the
table generated in a readable shape with its set of columns, making
unnecessary an update of gitattributes.
Reported-by: Peter Eisentraut
Author: John Naylor
Discussion: https://postgr.es/m/d601b3b5-a3c7-5457-2f84-3d6513d690fc@2ndquadrant.com
The previous set of multipliers was not adapted for large sets of short
keys, and this new set of multipliers allows to generate perfect hash
functions for larger sets without having an impact for existing callers
of those functions, as experimentation has showed. A future commit will
make use of that to improve the performance of unicode normalization.
All multipliers compile to shift-and-add instructions on most platforms.
This has been tested as far back as gcc 4.1 and clang 3.8.
Author: John Naylor
Reviewed-by: Mark Dilger, Michael Paquier
Discussion: https://postgr.es/m/CACPNZCt4fbJ0_bGrN5QPt34N4whv=mszM0LMVQdoa2rC9UMRXA@mail.gmail.com
While C is happy to cast "const void *" to "const unsigned char *"
silently, C++ insists on an explicit cast. Since we put these
functions into header files, cpluspluscheck whines about that.
Add the cast to pacify it.
Discussion: https://postgr.es/m/b517ec3918d645eb950505eac8dd434e@gaz-is.ru
We've been speculating for a long time that hash-based keyword lookup
ought to be faster than binary search, but up to now we hadn't found
a suitable tool for generating the hash function. Joerg Sonnenberger
provided the inspiration, and sample code, to show us that rolling our
own generator wasn't a ridiculous idea. Hence, do that.
The method used here requires a lookup table of approximately 4 bytes
per keyword, but that's less than what we saved in the predecessor commit
afb0d0712, so it's not a big problem. The time savings is indeed
significant: preliminary testing suggests that the total time for raw
parsing (flex + bison phases) drops by ~20%.
Patch by me, but it owes its existence to Joerg Sonnenberger;
thanks also to John Naylor for review.
Discussion: https://postgr.es/m/20190103163340.GA15803@britannica.bec.de
Bruce Momjian
John Naylor
Michael Paquier
Tom Lane