add warnings are arrays have bad strides

gridder_cxx.h

@@ -112,6 +112,14 @@ template<typename T, size_t ndim> class mav
     ptrdiff_t stride(size_t i) const { return str[i]; }
     T *data() const
       { return d; }
+    bool last_contiguous() const
+      { return (str[ndim-1]==1) || (str[ndim-1]==0); }
+    void check_storage(const char *name) const
+      {
+      if (!last_contiguous())
+        cout << "Array '" << name << "': last dimension is not contiguous.\n"
+                "This may slow down computation significantly!\n";
+      }
     bool contiguous() const
       {
       ptrdiff_t stride=1;
@@ -954,6 +962,8 @@ template<class T, class T2> class MsServ
       : baselines(baselines_), idx(idx_), ms(ms_), wgt(wgt_),
         nvis(idx.shape(0)), have_wgt(wgt.size()!=0)
       {
+      wgt.check_storage("wgt");
+      ms.check_storage("ms");
       checkShape(ms.shape(), {baselines.Nrows(), baselines.Nchannels()});
       if (have_wgt) checkShape(wgt.shape(), ms.shape());
       }