isInCircleAdapt sketch Java port

[Komzpa]

Do the non-robust calculation and calculation of error margin. If calculation is possibly not robust, fall back on slower math.

https://www.cs.cmu.edu/afs/cs/project/quake/public/code/predicates.c

References #298

[dr-jts]

Should call inCircleDDFast - it is equivalent and faster

[dr-jts]

Need unit tests before rolling this in.

[dr-jts]

Good find. This should provide both performance and robustness.

The same approach is currently used in computing the orientationIndex. Also based on Shewchuk's fine work.

[Komzpa]

Just in case, I would be happy if someone familiar with java takes over this PR, to make proper formatting, unit tests and code style.

[dr-jts]

Makes sense. And add some unit tests. Not sure when I'll have time to work on this though.

[grootstebozewolf]

Thanks for keeping this open — design-history note from the NetTopologySuite.Proofs mesh / Delaunay lane (we treated #311 → #1094 → #1212 as one product lineage; tip for merge discussion is #1212).

What this PR established (2018)

Stage A Shewchuk in-circle filter (coords translated so P is origin) with permanent-scaled iccerrboundA, then escalate when uncertain. That filter-then-escalate shape is exactly what #1212 and #1094 still use. Maintainer notes from 2018 (isInCircleDDFast, unit tests) aged well.

Numbers (Stage A only vs extracted b64_inCircle)

Write-up: jts-311-incircle-lane (oracle/jts311_incircle_history.txt, 22 vectors).

Check	Result
Oracle flip pin	POS 1.5
Stage A#311 CERTAIN vs oracle sign conflicts	0
Stage A#311 UNCERTAIN	7 (correct declines)

GEOS955 / JTS#1171 subset still shows why escalation exists: Stage A ZERO/UNCERTAIN, oracle POS.

Two archive notes (not merge blockers for a history PR)

1. Name vs body: isInCircleAdapt here is Stage A + DDFast, not Shewchuk’s full incircleadapt expansion stages (that fuller port is Make isInCircleRobust robust #1094).
2. ε: this PR uses Math.ulp(1.0) (= (2^{-52})); Shewchuk / Improve triangulation robustness #1212 / Make isInCircleRobust robust #1094 use (2^{-53}). Bound is ~2× looser (more DD). Direction is safe; later PRs align with the published constant.
3. 2026 large-coord unit test: after binary64 rounding of the (10^{14}) literals, Stage A det and the Rocq in-circle kernel both say ZERO (not strictly inside). If isInCircleDDFast still returns true on those doubles, that is a useful DD-path check against an independent kernel — happy to dig further if useful.

Bottom line

Valuable as the first open sketch of robust in-circle Stage A in JTS. For production merge we point at #1212 (Stage A + DDNormalized + Vertex.isCCW → Orientation.index); corpus gates for the tip are already green.

(Affiliation: NetTopologySuite.Proofs — formal mesh/predicate companion, not a JTS committer review.)