Before searching, foldCase the first up to 256 characters, and use this
buffer to compare against the haystack. If the needle is larger than the
buffer, compare the rest of the needle against the rest of the haystack
for every potential match. The buffer is placed on the stack and must be
refolded for each search, but this change does not break the API.
This is faster than the old implementation, except if the needle is long
and it is found near the beginning of the haystack, or if the needle is
long and it is not found in a short haystack where few comparisons are
done and hence few case foldings were needed in the old implementation.
Benchmarking using tst_bench_qstringtokenizer tokenize_qstring_qstring
shows an improvement for the the total testcase and usually for each
individual test.
Fixes: QTBUG-100239
Change-Id: Ie61342eb5c19f32de3c1ba0a51dbb0db503bdf3a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
d8387fc538