Replaces the per-call `representAsChecked<int>()` optional/`tassert` round-trip in `computeDiscreteRank()` — the rank helper shared by `DiscretePercentile` and `TDigest`. This is run once per requested `$percentile` — with an `isfinite`-guarded `static_cast` (behavior identical for every input `parseP()` admits). sys-perf A/B measured `percentiles_expr` +20–30% on master (both classic and SBE execution engines) and `array_10_percentile_many100` −19% → +19% vs 8.2 on v8.3.