In mixed or double mode, don't select devices that don't support double

platforms/opencl/src/OpenCLContext.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) 2009-2015 Stanford University and the Authors.      *
+ * Portions copyright (c) 2009-2016 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -113,6 +113,11 @@ OpenCLContext::OpenCLContext(const System& system, int platformIndex, int device
                     continue;
                 if (platformVendor == "Apple" && (devices[i].getInfo<CL_DEVICE_TYPE>() == CL_DEVICE_TYPE_CPU))
                     continue; // The CPU device on OS X won't work correctly.
+                if (useMixedPrecision || useDoublePrecision) {
+                    bool supportsDouble = (devices[i].getInfo<CL_DEVICE_EXTENSIONS>().find("cl_khr_fp64") != string::npos);
+                    if (!supportsDouble)
+                        continue; // This device does not support double precision.
+                }
                 int maxSize = devices[i].getInfo<CL_DEVICE_MAX_WORK_ITEM_SIZES>()[0];
                 int processingElementsPerComputeUnit = 8;
                 if (devices[i].getInfo<CL_DEVICE_TYPE>() != CL_DEVICE_TYPE_GPU) {