Add warning of possible overflow.

include/openmc/constants.h

@@ -339,6 +339,11 @@ enum class RunMode {
 
 enum class GeometryType { CSG, DAG };
 
+//==============================================================================
+// Volume Calculation Constants
+
+constexpr size_t SIZE_T_MAX {std::numeric_limits<size_t>::max()};
+
 } // namespace openmc
 
 #endif // OPENMC_CONSTANTS_H

src/volume_calc.cpp

@@ -225,6 +225,13 @@ vector<VolumeCalculation::Result> VolumeCalculation::execute() const
     iterations++;
     size_t total_samples = iterations * n_samples_;
 
+    // warn user if total sample size is greater than what the size_t type can
+    // represent
+    if (total_samples > SIZE_T_MAX) {
+      warning("The number of samples has exceeded the size_t type. Volume "
+              "results may be inaccurate.");
+    }
+
     // reset
     double trigger_val = -INFTY;