NNUE: re-fit raw-to-score calibration, NNU4 weight format, super-lazy default-on, lazy probe measured net-negative

Fits an affine (a + b*raw) correction into every exported .nnue file
(export_nnue_weights.py's CalibrateScoreMapping) so the engine's
consumed centipawn output tracks Stockfish's real score scale rather
than the net's nominal raw WDL-sigmoid output -- training variance
alone shifts this mapping across retrains even with an identical
recipe, so it's re-fit and baked in per export rather than assumed
constant. Weight format bumped to "NNU4" to carry the two new floats;
older NNU1/2/3 files are no longer readable.

Super-lazy (material-only) pre-filter promoted to default-on
(g_fUseNnueSuperLazy = TRUE) with a recalibrated per-material-bucket
margin table (measured against the recalibrated net, 16-shard
cross_sectional_200k.ep_ sample) -- real, measured nps win across all
three curated suites. The separate lazy-probe gate (accumulator-based
early exit) is measured net-negative on real search traffic at this
net's probe-vs-forward latency ratio and stays off by default
(g_fUseNnueLazyProbe = FALSE); code kept live since margin tuning
could still flip this, per docs/NNUE.md.

Also: direct per-call latency instrumentation for NnueProbeScore/
NnueForward (root.c, EVAL_TIME build) to make the lazy-probe
breakeven math measurable directly instead of inferred; QSearch
futility margins given real-data-derived NNUE_FULL/NNUE_LAZY
starting points.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

1 files changed, 25 insertions, 0 deletions

diff --git a/src/chess.h b/src/chess.h
index 3e65e7f..34099b2 100755
--- a/src/chess.h
+++ b/src/chess.h
@@ -1431,6 +1431,25 @@ typedef struct _COUNTERS
         UINT64 u64CyclesSuperLazyExit;
         UINT64 u64CyclesLazyExit;
         UINT64 u64CyclesFullEvalExit;
+
+        // 2026-10-20: direct per-call latency of the two NNUE eval
+        // primitives (nnueeval.c), as opposed to the HCE-oriented
+        // whole-path-cost counters above (which NNUE's Eval() branch
+        // doesn't feed -- it's gated on g_fUseNnueEval at runtime, not
+        // #ifdef LAZY_EVAL). u64CyclesNnueProbeCall/u64CyclesNnueForwardCall
+        // time just the TIMED_EVAL_CALL-wrapped NnueProbeScore()/
+        // NnueForward() calls themselves (eval.c's production NNUE
+        // branch); u64NnueProbeAttempts counts every probe call made
+        // (hit or miss) -- unlike u64LazyEvals, which only counts
+        // hits -- needed as the denominator for a true avg-cost-per-
+        // attempt (the question that actually matters for judging
+        // whether the gate pays for itself: cost is paid on every
+        // attempt, the saving only on a hit). u64FullEvals already
+        // counts NnueForward calls 1:1 on this path, so no separate
+        // attempt counter is needed for it.
+        UINT64 u64CyclesNnueProbeCall;
+        UINT64 u64CyclesNnueForwardCall;
+        UINT64 u64NnueProbeAttempts;
     }
     tree;
 
@@ -2378,6 +2397,12 @@ extern CHAR g_rgfNnueFc3Weight[NNUE_L3];
 extern float g_rgfNnueFc3Bias;
 extern float g_rgfNnueActScale[3];
 extern float g_rgfNnueWeightScale[3];
+// Affine raw-to-real-score correction (a + b*raw), re-fit and baked
+// into every export by CalibrateScoreMapping -- see nnueeval.c's
+// declaration comment and the 2026-10-20 "keeping this stable across
+// retrains" conversation. Defaults (0,1) are the identity transform.
+extern float g_fNnueCalibA;
+extern float g_fNnueCalibB;
 extern FLAG g_fNnueWeightsLoaded;
 extern FLAG g_fUseNnueEval;