Modify the static null move pruning, increasing depth and using eval progression.

alcides-schulz · alcides-schulz · commit 30ab6db7a8cd · 2025-05-20T08:03:09.000-04:00
20s+0.2 Hash=16
Score of tucanoNEW vs tucanoOLD: 1168 - 1088 - 2651  [0.508] 4907
Elo difference: 5.7 +/- 6.6, LOS: 95.4 %, DrawRatio: 54.0 %
SPRT: llr 2.95 (100.0%), lbound -2.94, ubound 2.94 - H1 was accepted

60s+0.6 Hash=64
Score of tucanoNEW vs tucanoOLD: 1811 - 1750 - 4332  [0.504] 7893
Elo difference: 2.7 +/- 5.1, LOS: 84.7 %, DrawRatio: 54.9 %
SPRT: llr 2.29 (77.7%), lbound -2.94, ubound 2.94

Score of tucanoNEW vs tucanoOLD: 1342 - 1263 - 3142  [0.507] 5747
Elo difference: 4.8 +/- 6.0, LOS: 93.9 %, DrawRatio: 54.7 %
SPRT: llr 2.95 (100.2%), lbound -2.94, ubound 2.94 - H1 was accepted
diff --git a/src/main.c b/src/main.c
@@ -20,7 +20,7 @@
 
 #define ENGINE "Tucano"
 #define AUTHOR "Alcides Schulz"
-#define VERSION "12.12"
+#define VERSION "12.13"
 
 void        develop_workbench(void);
 double      bench(int depth, int print);
diff --git a/src/search.c b/src/search.c
@@ -17,9 +17,6 @@
 
 #include "globals.h"
 
-#define STAT_NULL_DEPTH 4
-static int STAT_NULL_MARGIN[STAT_NULL_DEPTH] = { 0, 80, 160, 320 };
-
 #define RAZOR_DEPTH 6
 static int RAZOR_MARGIN[RAZOR_DEPTH] = { 0, 250, 500, 750, 1000, 1250 };
 
@@ -150,9 +147,12 @@ int search(GAME *game, UINT incheck, int alpha, int beta, int depth, MOVE exclud
         }
 
         // Static null move: eval score + margin is higher that current beta, so it can skip the search.
-        if (depth < STAT_NULL_DEPTH && eval_score - STAT_NULL_MARGIN[depth] >= beta && !is_losing_score(beta)) {
+        if (depth <= 6 && eval_score >= beta && !is_losing_score(beta)) {
             if (trans_move == MOVE_NONE || move_is_capture(trans_move)) {
-                return eval_score - STAT_NULL_MARGIN[depth];
+                int stat_null_margin = 100 * depth - improving * 80 - opponent_worsening * 30 + (ply > 0 ? game->eval_hist[ply - 1] / 350 : 0);
+                if (eval_score - stat_null_margin >= beta) {
+                    return eval_score - stat_null_margin;
+                }
             }
         }
 

Original file line number	Diff line number	Diff line change
`@@ -17,9 +17,6 @@`
`17`	`17`
`18`	`18`	`#include "globals.h"`
`19`	`19`
`20`		`-#define STAT_NULL_DEPTH 4`
`21`		`-static int STAT_NULL_MARGIN[STAT_NULL_DEPTH] = { 0, 80, 160, 320 };`
`22`		`-`
`23`	`20`	`#define RAZOR_DEPTH 6`
`24`	`21`	`static int RAZOR_MARGIN[RAZOR_DEPTH] = { 0, 250, 500, 750, 1000, 1250 };`
`25`	`22`
`@@ -150,9 +147,12 @@ int search(GAME *game, UINT incheck, int alpha, int beta, int depth, MOVE exclud`
`150`	`147`	`}`
`151`	`148`
`152`	`149`	`// Static null move: eval score + margin is higher that current beta, so it can skip the search.`
`153`		`- if (depth < STAT_NULL_DEPTH && eval_score - STAT_NULL_MARGIN[depth] >= beta && !is_losing_score(beta)) {`
	`150`	`+ if (depth <= 6 && eval_score >= beta && !is_losing_score(beta)) {`
`154`	`151`	`if (trans_move == MOVE_NONE \|\| move_is_capture(trans_move)) {`
`155`		`- return eval_score - STAT_NULL_MARGIN[depth];`
	`152`	`+ int stat_null_margin = 100 * depth - improving * 80 - opponent_worsening * 30 + (ply > 0 ? game->eval_hist[ply - 1] / 350 : 0);`
	`153`	`+ if (eval_score - stat_null_margin >= beta) {`
	`154`	`+ return eval_score - stat_null_margin;`
	`155`	`+ }`
`156`	`156`	`}`
`157`	`157`	`}`
`158`	`158`