unexpected speedup

gridder_cxx.h

@@ -672,7 +672,7 @@ class GridderConfig
         grid.data(), grid.data(), T(1), nthreads);
       }
 
-    template<typename T>void getpix(T u_in, T v_in, T &u, T &v, int &iu0, int &iv0) const
+    void getpix(double u_in, double v_in, double &u, double &v, int &iu0, int &iv0) const
       {
       u=fmod1(u_in*psx)*nu,
       iu0 = int(u-supp*0.5 + 1 + nu) - nu;
@@ -729,7 +729,7 @@ template<typename T, typename T2=complex<T>> class Helper
 
     vector<T2> rbuf, wbuf;
     bool do_w_gridding;
-    T w0, xdw;
+    double w0, xdw;
     size_t nexp;
     size_t nvecs;
 
@@ -776,9 +776,9 @@ template<typename T, typename T2=complex<T>> class Helper
     T kernel[64] ALIGNED(64);
 
     Helper(const GridderConfig &gconf_, const T2 *grid_r_, T2 *grid_w_,
-      T w0_=-1, T dw_=-1)
+      double w0_=-1, double dw_=-1)
       : gconf(gconf_), nu(gconf.Nu()), nv(gconf.Nv()), nsafe(gconf.Nsafe()),
-        supp(gconf.Supp()), beta(gconf.Beta()), grid_r(grid_r_),
+        supp(gconf.Supp()), beta(T(gconf.Beta())), grid_r(grid_r_),
         grid_w(grid_w_), su(2*nsafe+(1<<logsquare)), sv(2*nsafe+(1<<logsquare)),
         bu0(-1000000), bv0(-1000000),
         rbuf(su*sv*(grid_r!=nullptr),T(0)),
@@ -795,18 +795,18 @@ template<typename T, typename T2=complex<T>> class Helper
     T Wfac() const { return kernel[2*supp]; }
     void prep(const UVW &in)
       {
-      T u, v;
-      gconf.getpix<T>(in.u, in.v, u, v, iu0, iv0);
-      T xsupp=T(2)/supp;
-      auto x0 = xsupp*(iu0-u);
-      auto y0 = xsupp*(iv0-v);
+      double u, v;
+      gconf.getpix(in.u, in.v, u, v, iu0, iv0);
+      double xsupp=2./supp;
+      double x0 = xsupp*(iu0-u);
+      double y0 = xsupp*(iv0-v);
       for (int i=0; i<supp; ++i)
         {
-        kernel[i  ] = x0+i*xsupp;
-        kernel[i+supp] = y0+i*xsupp;
+        kernel[i  ] = T(x0+i*xsupp);
+        kernel[i+supp] = T(y0+i*xsupp);
         }
       if (do_w_gridding)
-        kernel[2*supp] = min(T(1), xdw*xsupp*abs(w0-T(in.w)));
+        kernel[2*supp] = min(T(1), T(xdw*xsupp*abs(w0-in.w)));
       for (size_t i=nexp; i<nvecs; ++i)
         kernel[i]=0;
       for (size_t i=0; i<nvecs; ++i)
@@ -1196,12 +1196,12 @@ template<typename T> void apply_wcorr(const GridderConfig &gconf,
       {
       double fy = y0+j*psy;
       fy*=fy;
-      double fct = 0;
+      T fct = 0;
       double tmp = 1.-fx-fy;
       if (tmp>=0)
         {
         auto nm1 = (-fx-fy)/(sqrt(1.-fx-fy)+1.); // accurate form of sqrt(1-x-y)
-        fct = (nm1<=-1) ? 0. : kernel.corfac(nm1*dw);
+        fct = T((nm1<=-1) ? 0. : kernel.corfac(nm1*dw));
         }
       size_t i2 = nx_dirty-i, j2 = ny_dirty-j;
       dirty(i,j)*=fct;