Fixed calculation of bandwidth for big dataset sizes

tests/benchmarks/spmv.h

@@ -139,7 +139,7 @@ benchmarkSpMV( Benchmark & benchmark,
 
     const int elements = setHostTestMatrix< HostMatrix >( hostMatrix, elementsPerRow );
     setCudaTestMatrix< DeviceMatrix >( deviceMatrix, elementsPerRow );
-    const double datasetSize = loops * elements * ( 2 * sizeof( Real ) + sizeof( int ) ) / oneGB;
+    const double datasetSize = ( double ) loops * elements * ( 2 * sizeof( Real ) + sizeof( int ) ) / oneGB;
 
     // reset function
     auto reset = [&]() {