Fixed an edge condition that could cause errors in CMAPTorsionForce

platforms/common/src/kernels/cmapTorsionForce.cc

@@ -61,8 +61,8 @@ angleB = fmod(angleB+2.0f*PI, 2.0f*PI);
 int2 pos = MAP_POS[MAPS[index]];
 int size = pos.y;
 real delta = 2*PI/size;
-int s = (int) (angleA/delta);
-int t = (int) (angleB/delta);
+int s = (int) fmin(angleA/delta, size-1);
+int t = (int) fmin(angleB/delta, size-1);
 float4 c[4];
 int coeffIndex = pos.x+4*(s+size*t);
 c[0] = COEFF[coeffIndex];

platforms/reference/src/SimTKReference/ReferenceCMAPTorsionIxn.cpp

 
-/* Portions copyright (c) 2010-2016 Stanford University and Simbios.
+/* Portions copyright (c) 2010-2020 Stanford University and Simbios.
  * Contributors: Peter Eastman
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -133,8 +133,8 @@ void ReferenceCMAPTorsionIxn::calculateOneIxn(int index, vector<Vec3>& atomCoord
 
     int size = (int) sqrt(coeff[map].size());
     double delta = 2*M_PI/size;
-    int s = (int) (angleA/delta);
-    int t = (int) (angleB/delta);
+    int s = (int) fmin(angleA/delta, size-1);
+    int t = (int) fmin(angleB/delta, size-1);
     const vector<double>& c = coeff[map][s+size*t];
     double da = angleA/delta-s;
     double db = angleB/delta-t;