Fixed numeric overflow (#4650)

platforms/cpu/src/CpuSETTLE.cpp

@@ -6,7 +6,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2013-2018 Stanford University and the Authors.      *
+ * Portions copyright (c) 2013-2024 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -37,13 +37,13 @@ using namespace std;
 
 CpuSETTLE::CpuSETTLE(const System& system, const ReferenceSETTLEAlgorithm& settle, ThreadPool& threads) : threads(threads) {
     int numBlocks = 10*threads.getNumThreads();
-    int numClusters = settle.getNumClusters();
+    long long numClusters = settle.getNumClusters();
     vector<double> mass(system.getNumParticles());
     for (int i = 0; i < system.getNumParticles(); i++)
         mass[i] = system.getParticleMass(i);
     for (int i = 0; i < numBlocks; i++) {
-        int start = i*numClusters/numBlocks;
-        int end = (i+1)*numClusters/numBlocks;
+        int start = (int) (i*numClusters/numBlocks);
+        int end = (int) ((i+1)*numClusters/numBlocks);
         if (start != end) {
             int numThreadClusters = end-start;
             vector<int> atom1(numThreadClusters), atom2(numThreadClusters), atom3(numThreadClusters);