- Don’t expose the raw execution seed to _rawHashValue.
- Change the type of _rawHashValue’s seed from (UInt64,UInt64) to a single Int. Working with a pair of UInt64s is unwieldy, and overkill in practice. Int as a seed also integrates nicely with Int as a hash value.
- Remove _HasherCore._generateSeed(). Instead, simply call finalize() on a copy of the hasher to get a seed suitable for _rawHashValue.
- Update Set and Dictionary to store a single Int as the seed value.
Note that this doesn’t affect the core hasher, which still mixes in the actual 128-bit execution seed during its initialization. To reduce the potential of confusion, use the name “rawSeed” to refer to an actual 128-bit seed value.
The new _rawHashValue(seed:) requirement allows stdlib types to specialize their hashing when they’re hashed on their own (i.e., not as a component of some composite type).
This makes it possible to get rid of discriminator/terminator values and to eliminate most of Hasher’s resiliency overhead, leading to a measurable speedup, especially for tiny keys.
Newly internal declarations include Hasher._seed and the integer overloads of Hasher._combine(_:), as well as _SipHash13 and _SipHash24.
Unify the interfaces of these SipHash testing structs with Hasher. Update SipHash test to cover Hasher, too.
Add @usableFromInline to all newly internal stuff. In addition to its normal use, it also enables white box testing; compile tests that need to use these declarations with -disable-access-control.
