Rewrite _EvalKing as a linear ring-scan and promote its terms to DNA-tunable constants; retune via mate-mining regression, ElasticNet/Ridge, and logistic-vs-material refits.

Splits _EvalKing's own king-location table from CountKingSafetyDefects' search-gate copy so future eval retunes can't silently perturb extension/reduction gate frequency. Bumps KING_BACK_FLIGHT_BONUS (+1 -> +3) and reorders/nudges the ring-scan sub-terms (minor/pawn/xray/undefended) to match relative rankings that replicated across three independent calibration methods, while leaving KING_QUEEN_PROXIMITY_DANGER and KING_MISSING_ONE_CASTLE_OPTION untouched pending further discussion.

Self-play (640 games) is roughly even (score 0.509, llr=+0.17, far from either SPRT bound) but consistently faster (nps candidate=1362140 vs head=1333682) at equal average depth -- landing as a wash/speed-neutral checkpoint, not a confirmed tactical improvement, for further tuning to build on.

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

1 files changed, 48 insertions, 1 deletions

diff --git a/src/data.c b/src/data.c
index 7c84b1a..71a1531 100644
--- a/src/data.c
+++ b/src/data.c
@@ -750,13 +750,21 @@ Return value:
 //
 BITBOARD g_KingAttacksBB[128];
 
+// 2026-09-15: see chess.h's comment on these three. Deltas below match
+// eval.c's old KingSafetyDeltas exactly (front = -17/-16/-15 for WHITE,
+// +15/+16/+17 for BLACK; side = -1/+1, color-independent).
+BITBOARD g_KingRingFrontBB[2][128];
+BITBOARD g_KingRingBackBB[2][128];
+BITBOARD g_KingRingSideBB[128];
+
 void
 InitializeKingAttackTables(void)
 /**
 
 Routine description:
 
-    One-time startup init for g_KingAttacksBB -- see its comment.
+    One-time startup init for g_KingAttacksBB and the front/back/side
+    ring-bitboard split -- see their comments.
 
 Parameters:
 
@@ -770,8 +778,23 @@ Return value:
 {
     ULONG uRank, uFile, uDir;
     COOR c, cSquare;
+    static const int iFrontDeltas[2][3] =
+    {
+        { +15, +16, +17 },  // BLACK
+        { -17, -16, -15 },  // WHITE
+    };
+    static const int iBackDeltas[2][3] =
+    {
+        { -17, -16, -15 },  // BLACK
+        { +15, +16, +17 },  // WHITE
+    };
+    static const int iSideDeltas[2] = { -1, +1 };
+    ULONG uColor, uFrontBackSlot, uSideSlot;
 
     memset(g_KingAttacksBB, 0, sizeof(g_KingAttacksBB));
+    memset(g_KingRingFrontBB, 0, sizeof(g_KingRingFrontBB));
+    memset(g_KingRingBackBB, 0, sizeof(g_KingRingBackBB));
+    memset(g_KingRingSideBB, 0, sizeof(g_KingRingSideBB));
     for (uRank = 0; uRank < 8; uRank++)
     {
         for (uFile = 0; uFile < 8; uFile++)
@@ -785,6 +808,30 @@ Return value:
                     g_KingAttacksBB[c] |= COOR_TO_BB(cSquare);
                 }
             }
+            for (uColor = 0; uColor < 2; uColor++)
+            {
+                for (uFrontBackSlot = 0; uFrontBackSlot < 3; uFrontBackSlot++)
+                {
+                    cSquare = c + iFrontDeltas[uColor][uFrontBackSlot];
+                    if (IS_ON_BOARD(cSquare))
+                    {
+                        g_KingRingFrontBB[uColor][c] |= COOR_TO_BB(cSquare);
+                    }
+                    cSquare = c + iBackDeltas[uColor][uFrontBackSlot];
+                    if (IS_ON_BOARD(cSquare))
+                    {
+                        g_KingRingBackBB[uColor][c] |= COOR_TO_BB(cSquare);
+                    }
+                }
+            }
+            for (uSideSlot = 0; uSideSlot < 2; uSideSlot++)
+            {
+                cSquare = c + iSideDeltas[uSideSlot];
+                if (IS_ON_BOARD(cSquare))
+                {
+                    g_KingRingSideBB[c] |= COOR_TO_BB(cSquare);
+                }
+            }
         }
     }
 }