From f78699ac21170da40dbbf05735134e0cc59199f2 Mon Sep 17 00:00:00 2001
From: Martin Reinecke <martin@mpa-garching.mpg.de>
Date: Wed, 30 Oct 2019 14:06:29 +0100
Subject: [PATCH] try to make index calculation parallel

---
 gridder_cxx.h    | 190 ++++++++++++++++++++++++++++++++++++++++++++++-
 nifty_gridder.cc |  15 ++++
 2 files changed, 201 insertions(+), 4 deletions(-)

diff --git a/gridder_cxx.h b/gridder_cxx.h
index 14a013a..06f1f15 100644
--- a/gridder_cxx.h
+++ b/gridder_cxx.h
@@ -1618,6 +1618,20 @@ void fillIdx(const Baselines &baselines,
           res[acc[tmp[idx++]]++] = baselines.getIdx(irow, ichan);
         }
   }
+class SimpleTimer
+  {
+  private:
+    using clock = std::chrono::steady_clock;
+    clock::time_point starttime;
+
+  public:
+    SimpleTimer()
+      : starttime(clock::now()) {}
+    double operator()() const
+      {
+      return std::chrono::duration<double>(clock::now() - starttime).count();
+      }
+  };
 
 template<typename T> vector<idx_t> getWgtIndices(const Baselines &baselines,
   const GridderConfig &gconf, const const_mav<T,2> &wgt)
@@ -1631,9 +1645,19 @@ template<typename T> vector<idx_t> getWgtIndices(const Baselines &baselines,
   size_t nbu = (gconf.Nu()+1+side-1) >> logsquare,
          nbv = (gconf.Nv()+1+side-1) >> logsquare;
   vector<idx_t> acc(nbu*nbv+1, 0);
-  vector<idx_t> tmp(nrow*nchan);
+  vector<idx_t> tmp(nrow*nchan,~idx_t(0));
 
-  for (idx_t irow=0, idx=0; irow<nrow; ++irow)
+#pragma omp parallel
+{
+  idx_t nthr = my_num_threads();
+  idx_t id = my_thread_num();
+  idx_t nbase = nrow/nthr;
+  idx_t additional = nrow%nthr;
+  idx_t lo = id*nbase + ((id<additional) ? id : additional);
+  idx_t hi = lo+nbase+(id<additional);
+  vector<idx_t> lacc(nbu*nbv+1, 0);
+
+  for (idx_t irow=lo, idx=lo*nchan; irow<hi; ++irow)
     for (idx_t ichan=0; ichan<nchan; ++ichan)
       if ((!have_wgt) || (wgt(irow,ichan)!=0))
         {
@@ -1644,18 +1668,25 @@ template<typename T> vector<idx_t> getWgtIndices(const Baselines &baselines,
         gconf.getpix(uvw.u, uvw.v, u, v, iu0, iv0);
         iu0 = (iu0+nsafe)>>logsquare;
         iv0 = (iv0+nsafe)>>logsquare;
-        ++acc[nbv*iu0 + iv0 + 1];
+        ++lacc[nbv*iu0 + iv0 + 1];
         tmp[idx++] = nbv*iu0 + iv0;
         }
-
+#pragma omp barrier
+#pragma omp critical(xyz)
+  for (size_t i=0; i<acc.size(); ++i)
+    acc[i]+=lacc[i];
+}
   for (size_t i=1; i<acc.size(); ++i)
     acc[i] += acc[i-1];
 
   vector<idx_t> res(acc.back());
   for (size_t irow=0, idx=0; irow<nrow; ++irow)
     for (size_t ichan=0; ichan<nchan; ++ichan)
+      {
+      while (tmp[idx]==idx_t(~0)) ++idx;
       if ((!have_wgt) || (wgt(irow,ichan)!=0))
         res[acc[tmp[idx++]]++] = baselines.getIdx(irow, ichan);
+      }
   return res;
   }
 
@@ -1684,6 +1715,156 @@ template<typename T> void dirty2ms(const const_mav<double,2> &uvw,
   dirty2x(gconf, dirty, makeMsServ(baselines,idx2,ms,wgt), do_wstacking, verbosity);
   }
 
+static const uint16_t utab[] = {
+#define Z(a) 0x##a##0, 0x##a##1, 0x##a##4, 0x##a##5
+#define Y(a) Z(a##0), Z(a##1), Z(a##4), Z(a##5)
+#define X(a) Y(a##0), Y(a##1), Y(a##4), Y(a##5)
+X(0),X(1),X(4),X(5)
+#undef X
+#undef Y
+#undef Z
+};
+
+uint32_t coord2morton2D_32 (uint32_t x, uint32_t y)
+  {
+  typedef uint32_t I;
+  return  (I)(utab[x&0xff])     | ((I)(utab[(x>>8)&0xff])<<16)
+       | ((I)(utab[y&0xff])<<1) | ((I)(utab[(y>>8)&0xff])<<17);
+  }
+
+static const uint8_t m2p2D_1[4][4] = {
+{ 4, 1, 11, 2},{0,15, 5, 6},{10,9,3,12},{14,7,13,8}};
+static uint8_t m2p2D_3[4][64];
+static const uint8_t p2m2D_1[4][4] = {
+{ 4, 1, 3, 10},{0,6,7,13},{15,9,8,2},{11,14,12,5}};
+static uint8_t p2m2D_3[4][64];
+static int peano2d_done=0;
+
+static void init_peano2d (void)
+  {
+  peano2d_done=1;
+
+  for (int d=0; d<4; ++d)
+    for (uint32_t p=0; p<64; ++p)
+      {
+      unsigned rot = d;
+      uint32_t v = p<<26;
+      uint32_t res = 0;
+      for (int i=0; i<3; ++i)
+        {
+        unsigned tab=m2p2D_1[rot][v>>30];
+        v<<=2;
+        res = (res<<2) | (tab&0x3);
+        rot = tab>>2;
+        }
+      m2p2D_3[d][p]=res|(rot<<6);
+      }
+  for (int d=0; d<4; ++d)
+    for (uint32_t p=0; p<64; ++p)
+      {
+      unsigned rot = d;
+      uint32_t v = p<<26;
+      uint32_t res = 0;
+      for (int i=0; i<3; ++i)
+        {
+        unsigned tab=p2m2D_1[rot][v>>30];
+        v<<=2;
+        res = (res<<2) | (tab&0x3);
+        rot = tab>>2;
+        }
+      p2m2D_3[d][p]=res|(rot<<6);
+      }
+  }
+
+uint32_t morton2peano2D_32(uint32_t v, int bits)
+  {
+  if (!peano2d_done) init_peano2d();
+  unsigned rot = 0;
+  uint32_t res = 0;
+  v<<=32-(bits<<1);
+  int i=0;
+  for (; i<bits-2; i+=3)
+    {
+    unsigned tab=m2p2D_3[rot][v>>26];
+    v<<=6;
+    res = (res<<6) | (tab&0x3fu);
+    rot = tab>>6;
+    }
+  for (; i<bits; ++i)
+    {
+    unsigned tab=m2p2D_1[rot][v>>30];
+    v<<=2;
+    res = (res<<2) | (tab&0x3);
+    rot = tab>>2;
+    }
+  return res;
+  }
+
+template<typename It, typename Comp> class IdxComp__
+  {
+  private:
+    It begin;
+    Comp comp;
+  public:
+    IdxComp__ (It begin_, Comp comp_): begin(begin_), comp(comp_) {}
+    bool operator() (std::size_t a, std::size_t b) const
+      { return comp(*(begin+a),*(begin+b)); }
+  };
+
+/*! Performs an indirect sort on the supplied iterator range and returns in
+    \a idx a \a vector containing the indices of the smallest, second smallest,
+    third smallest, etc. element, according to \a comp. */
+template<typename It, typename T2, typename Comp>
+  inline void buildIndex (It begin, It end, std::vector<T2> &idx, Comp comp)
+  {
+  using namespace std;
+  T2 num=end-begin;
+  idx.resize(num);
+  for (T2 i=0; i<num; ++i) idx[i] = i;
+  sort (idx.begin(),idx.end(),IdxComp__<It,Comp>(begin,comp));
+  }
+
+/*! Performs an indirect sort on the supplied iterator range and returns in
+    \a idx a \a vector containing the indices of the smallest, second smallest,
+    third smallest, etc. element. */
+template<typename It, typename T2> inline void buildIndex (It begin, It end,
+  std::vector<T2> &idx)
+  {
+  using namespace std;
+  typedef typename iterator_traits<It>::value_type T;
+  buildIndex(begin,end,idx,less<T>());
+  }
+
+void getRowOrdering(const const_mav<double,2> &uvw, const mav<idx_t,1> &idx)
+  {
+  myassert(uvw.shape(1)==3, "second dimension of uvw array must be 3");
+  size_t nrow = uvw.shape(0);
+  myassert(nrow>0, "zero-sized array");
+  myassert(nrow==idx.shape(0), "dimension mismatch");
+  double umin=uvw(0,0), umax=uvw(0,0), vmin=uvw(0,1), vmax=uvw(0,1);
+  for (size_t i=1; i<nrow; ++i)
+    {
+    umin=min(umin, uvw(i,0));
+    umax=max(umax, uvw(i,0));
+    vmin=min(vmin, uvw(i,1));
+    vmax=max(vmax, uvw(i,1));
+    }
+  constexpr size_t order=12;
+  constexpr size_t ncells=size_t(1)<<order;
+  double xdu = ncells/(umax-umin), xdv = ncells/(vmax-vmin);
+  vector<idx_t> peano(nrow);
+  for (size_t i=0; i<nrow; ++i)
+    {
+    size_t iu = min(ncells-1,size_t((uvw(i,0)-umin)*xdu));
+    size_t iv = min(ncells-1,size_t((uvw(i,1)-vmin)*xdv));
+    peano[i] = morton2peano2D_32(coord2morton2D_32(iu,iv), order);
+    }
+  vector<idx_t> tidx;
+  buildIndex(peano.begin(), peano.end(), tidx);
+  for (size_t i=0; i<nrow; ++i)
+    idx(i) = tidx[i];
+  }
+
 } // namespace detail
 
 // public names
@@ -1699,6 +1880,7 @@ using detail::vis2dirty;
 using detail::dirty2vis;
 using detail::ms2dirty;
 using detail::dirty2ms;
+using detail::getRowOrdering;
 using detail::streamDump__;
 using detail::CodeLocation;
 } // namespace gridder
diff --git a/nifty_gridder.cc b/nifty_gridder.cc
index c84f07b..332a6f5 100644
--- a/nifty_gridder.cc
+++ b/nifty_gridder.cc
@@ -1027,6 +1027,19 @@ py::array Pydirty2ms(const py::array &uvw,
   myfail("type matching failed: 'dirty' has neither type 'f4' nor 'f8'");
   }
 
+py::array PygetRowOrdering(const py::array &uvw_)
+  {
+  auto uvw = getPyarr<double>(uvw_, "uvw");
+  auto uvw2 = make_const_mav<2>(uvw);
+  auto res = makeArray<idx_t>({uvw2.shape(0)});
+  auto res2 = make_mav<1>(res);
+  {
+  py::gil_scoped_release release;
+  getRowOrdering(uvw2, res2);
+  }
+  return res;
+  }
+
 } // unnamed namespace
 
 PYBIND11_MODULE(nifty_gridder, m)
@@ -1117,4 +1130,6 @@ PYBIND11_MODULE(nifty_gridder, m)
   m.def("dirty2ms", &Pydirty2ms, dirty2ms_DS, "uvw"_a, "freq"_a, "dirty"_a,
     "wgt"_a=None, "pixsize_x"_a, "pixsize_y"_a, "epsilon"_a,
     "do_wstacking"_a=false, "nthreads"_a=1, "verbosity"_a=0);
+
+  m.def("getRowOrdering", &PygetRowOrdering, "uvw"_a);
   }
-- 
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