speedup via inplace processing

include/armadillo_bits/SpSubview_meat.hpp

@@ -354,7 +354,60 @@ SpSubview<eT>::operator%=(const Base<eT, T1>& x)
   {
   arma_extra_debug_sigprint();
   
-  return (*this).operator=( (*this) % x.get_ref() );
+  SpSubview<eT>& sv = (*this);
+  
+  const quasi_unwrap<T1> U(x.get_ref());
+  const Mat<eT>& B     = U.M;
+  
+  arma_debug_assert_same_size(sv.n_rows, sv.n_cols, B.n_rows, B.n_cols, "element-wise multiplication");
+  
+  SpMat<eT>& sv_m = access::rw(sv.m);
+  
+  sv_m.sync_csc();
+  sv_m.invalidate_cache();
+  
+  const uword m_row_start = sv.aux_row1;
+  const uword m_row_end   = sv.aux_row1 + sv.n_rows - 1;
+  
+  const uword m_col_start = sv.aux_col1;
+  const uword m_col_end   = sv.aux_col1 + sv.n_cols - 1;
+  
+  constexpr eT zero = eT(0);
+  
+  bool  has_zero = false;
+  uword count    = 0;
+  
+  for(uword m_col = m_col_start; m_col <= m_col_end; ++m_col)
+    {
+    const uword sv_col = m_col - m_col_start;
+    
+    const uword index_start = sv_m.col_ptrs[m_col    ];
+    const uword index_end   = sv_m.col_ptrs[m_col + 1];
+    
+    for(uword i=index_start; i < index_end; ++i)
+      {
+      const uword m_row = sv_m.row_indices[i];
+      
+      if(m_row < m_row_start)  { continue; }
+      if(m_row > m_row_end  )  { break;    }
+      
+      const uword sv_row = m_row - m_row_start;
+      
+      eT& m_val = access::rw(sv_m.values[i]);
+      
+      const eT result = m_val * B.at(sv_row, sv_col);
+      
+      m_val = result;
+      
+      if(result == zero)  { has_zero = true; } else { ++count; }
+      }
+    }
+  
+  if(has_zero)  { sv_m.remove_zeros(); }
+  
+  access::rw(sv.n_nonzero) = count;
+  
+  return (*this);
   }