Re: Performance improvement for large keysets

[Bruno Haible]

Hi Pavel,

> When gperf was way too slow for me to wait, I took a quick look with
> profiler and made a simple optimization in Search::compute_partition to
> avoid scanning all possible partitions and to consider only those with
> matching size.
> 
> Please consider taking the change:
> https://github.com/pps83/gperf/commit/5da97d6ac156f1fdb7967a9f45654c15ab9b4e83
> ...
> This change results in roughly 35% run-time speedup with 5000 keys (key
> lengths are 1 to 10 chars).

Probably it can be optimized even more, by using a hash table in this place
(mapping an undetermined_chars array to the list of keywords that have this
same undetermined_chars array)...

> This change uses std::vector, if you prefer not to introduce std c++
> containers, then you may take follow up change to use basic c++ code:
> https://github.com/pps83/gperf/commit/f967d3c1f63902e022dac586d646824d91ff21b7

Yes, so far gperf has seen very few portability hassles due to the evolution
of the C++ standard, because it hardly relies on the libstdc++ functionality.
The alternative is to buy into libstdc++, and then work around portability
problems through autoconf tests and #ifdef - which is a lot of effort for
the small codebase of gperf.

Bruno