SipHash is highly HashDoS-resistent, initialized with a random seed at
startup (i.e. non-deterministic) and usable for security-critical use
cases with large enough parameters. We just use it because it's
reasonably secure with parameters 1-3 while having excellent properties
and not being significantly slower than before.
This patch adds the `USING_AK_GLOBALLY` macro which is enabled by
default, but can be overridden by build flags.
This is a step towards integrating Jakt and AK types.
Currently, we define a CaseInsensitiveStringTraits structure for String.
Using this structure for StringView involves allocating a String from
that view, and a second string to convert that intermediate string to
lowercase.
This defines CaseInsensitiveStringViewTraits (and the underlying helper
case_insensitive_string_hash) to avoid allocations.
For some algorithms, such as bloom filters, it's possible to reuse a
hash function (rather than having different hashing functions) if the
seed is different each time the hash function is used.
Modify AK::string_hash() to take a seed parameter, which defaults to 0
(the value the hash value was originally initialized to).
Example failure:
IDAllocator.h only pulls in AK/Hashtable.h, so any compilation unit that
includes AK/IDAllocator.h without including AK/Traits.h before it used
to be doomed to fail with the cryptic error message "In instantiation of
'AK::HashTable<T, TraitsForT, IsOrdered>::Iterator AK::HashTable<T,
TraitsForT, IsOrdered>::find(const T&) [with T = int; TraitsForT =
AK::Traits: incomplete type 'AK::Traits<int>' used in nested name
specifier".
