Similar to commit 0652cc4, we now generate 2-stage lookup tables for
case conversion information. Only about 1500 code points are actually
cased. This means that case information is rather highly compressible,
as the blocks we break the code points into will generally all have no
casing information at all.
In total, this change:
* Does not change the size of libunicode.so (which is nice because,
generally, the 2-stage lookup tables are expected to trade a bit
of size for performance).
* Reduces the runtime of the new benchmark test case added here from
1.383s to 1.127s (about an 18.5% improvement).
We currently fully casefold the left- and right-hand sides to compare
two strings with case-insensitivity. Now, we casefold one code point at
a time, storing the result in a view for comparison, until we exhaust
both strings.
Case folding rules have a similar mapping style as special casing rules,
where one code point may map to zero or more case folding rules. These
will be used for case-insensitive string comparisons. To see how case
folding can differ from other casing rules, consider "ß" (U+00DF):
>>> "ß".lower()
'ß'
>>> "ß".upper()
'SS'
>>> "ß".title()
'Ss'
>>> "ß".casefold()
'ss'
And remove links that aren't adding much value but will often get out of
date (i.e. links to UCD files, which are already all listed in
unicode_data.cmake).
Unicode declares that to titlecase a string, the first cased code point
after each word boundary should be transformed to its titlecase mapping.
All other codepoints are transformed to their lowercase mapping.
