Simplify hashfull()

[mstembera]

STC https://tests.stockfishchess.org/tests/view/6719696086d5ee47d953cce6
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 79200 W: 20537 L: 20366 D: 38297
Ptnml(0-2): 267, 8736, 21387, 8979, 231

No functional change
bench: 1283457

[github-actions]

clang-format 18 needs to be run on this PR.
If you do not have clang-format installed, the maintainer will run it when merging.
For the exact version please see https://packages.ubuntu.com/noble/clang-format-18.

(execution 11805141837 / attempt 1)

[mstembera]

@Disservin Is there something this needs since it wasn't merged with the recent batch of patches?

[Disservin]

i'd prefer to leave this unchanged for better consistency with previous versions unless there is a real performance hit

[mstembera]

@Disservin Are you referring to the constant 1000 to 500 change or the code changes? The reason I'm confused about your consistency comment with previous versions is because the the current master version of hashfull() was only recently written in PR #5354 just to get something working for benchmark. It actually clumsily duplicates the existing functionality of TTEntry::relative_age() (which was nicely written by you in https://github.com/official-stockfish/Stockfish/pull/5061/files) instead of using it. Prior to #5354 hashfull() looked like (click link below)

Stockfish/src/tt.cpp

Line 196 in aff1f67

int TranspositionTable::hashfull() const {

which is much more consistent with this PR. Could you please take one more look and clarify? I will do whatever you decide of course. Thanks.

[Disservin]

the usage of the appropiate functions is good, I just mean the 500

[mstembera]

Ok the 500 is now reverted.
[Edit] Actually let me run it as an elo gainer first https://tests.stockfishchess.org/tests/view/6733bee386d5ee47d953e948