Fix integer division and boundary errors in scored-SGF near-end detection

cpp/command/runtests.cpp

@@ -52,6 +52,7 @@ int MainCmds::runtests(const vector<string>& args) {
   Tests::runBoardStressTest();
 
   Tests::runSgfTests();
+  Tests::runTrainingDataEndTests();
   Tests::runBasicSymmetryTests();
   Tests::runBoardSymmetryTests();
   Tests::runSymmetryDifferenceTests();

cpp/command/writetrainingdata.cpp

@@ -13,13 +13,54 @@
 #include "../program/play.h"
 #include "../command/commandline.h"
 #include "../core/test.h"
+#include "../tests/tests.h"
 #include "../main.h"
 
 #include <chrono>
 #include <csignal>
 
 using namespace std;
 
+// Keep this ownership gate independent of NN evaluation so its thresholds can be tested directly.
+static bool isNearEndByOwnership(
+  int boardArea, int blackWhiteVeryDifferent, int blackCountUnsettled, int whiteCountUnsettled
+) {
+  // count / boardArea < 0.10 + 6.0 / boardArea, compared exactly for positive board areas.
+  // Widen before scaling to avoid both integer truncation and floating-point boundary drift.
+  const int64_t maxScaledUnsettled = (int64_t)boardArea + 60;
+  return
+    10LL * blackWhiteVeryDifferent < maxScaledUnsettled
+    && 10LL * blackCountUnsettled < maxScaledUnsettled
+    && 10LL * whiteCountUnsettled < maxScaledUnsettled;
+}
+
+void Tests::runTrainingDataEndTests() {
+  cout << "Running scored-game near-end ownership tests" << endl;
+  struct TestCase {
+    int xSize;
+    int ySize;
+    int lastAllowedCount;
+  };
+  // Rectangles exercise exact thresholds that the fractional comparison can round upward.
+  // 10x10 also checks the strict comparison at the exact 16-point threshold.
+  const TestCase cases[] = {
+    {5,6,8}, {9,9,14}, {9,10,14}, {10,10,15}, {10,12,17},
+    {10,19,24}, {13,13,22}, {14,15,26}, {15,18,32}, {19,19,42}
+  };
+  for(const TestCase& testCase: cases) {
+    int boardArea = testCase.xSize * testCase.ySize;
+    // Sweep zero, both sides of the threshold, half the board, and the full board.
+    // Each counter must reject independently, even when the other two are zero.
+    for(int count = 0; count <= boardArea; count++) {
+      bool expected = count <= testCase.lastAllowedCount;
+      testAssert(isNearEndByOwnership(boardArea,count,0,0) == expected);
+      testAssert(isNearEndByOwnership(boardArea,0,count,0) == expected);
+      testAssert(isNearEndByOwnership(boardArea,0,0,count) == expected);
+      testAssert(isNearEndByOwnership(boardArea,count,count,count) == expected);
+    }
+  }
+}
+
 static ValueTargets makeForcedWinnerValueTarget(Player winner) {
   ValueTargets targets;
   if(winner == C_EMPTY) {
@@ -2028,7 +2069,6 @@ int MainCmds::writetrainingdata(const vector<string>& args) {
         double winlossDiff = abs(valuesIfBlackFirst.winLossValue - valuesIfWhiteFirst.winLossValue);
         // Remaining difference between side to move is less than 4 pointsish, and the winrate is close
         if(leadDiff < 3.5 + 0.05 * absAvgLead && winlossDiff < 0.2) {
-          const double maxFractionOfBoardUnsettled = 0.10 + 6.0 / boardArea;
           int blackCountUnsettled = 0;
           int whiteCountUnsettled = 0;
           int blackWhiteVeryDifferent = 0;
@@ -2043,13 +2083,9 @@ int MainCmds::writetrainingdata(const vector<string>& args) {
                 blackWhiteVeryDifferent += 1;
             }
           }
-          if(
-            blackWhiteVeryDifferent / boardArea < maxFractionOfBoardUnsettled
-            && blackCountUnsettled / boardArea < maxFractionOfBoardUnsettled
-            && whiteCountUnsettled / boardArea < maxFractionOfBoardUnsettled
-          ) {
-            gameIsNearEnd = true;
-          }
+          gameIsNearEnd = isNearEndByOwnership(
+            boardArea,blackWhiteVeryDifferent,blackCountUnsettled,whiteCountUnsettled
+          );
         }
       }
 

cpp/tests/tests.h

@@ -69,6 +69,9 @@ namespace Tests {
   //testtime.cpp
   void runTimeControlsTests();
 
+  //command/writetrainingdata.cpp
+  void runTrainingDataEndTests();
+
   //testtrainingwrite.cpp
   void runTrainingWriteTests();
   void runPassAliveSuicideGameTests();