From 7dc8e9a1f4b9413192d7ea893dd117af67073e17 Mon Sep 17 00:00:00 2001
From: Peter Munch <peterrmuench@gmail.com>
Date: Sun, 20 Mar 2022 08:25:46 +0100
Subject: [PATCH] ConstraintKinds: compress/decompress

---
 .../matrix_free/hanging_nodes_internal.h      | 71 ++++++++++++++++++-
 tests/matrix_free/hanging_node_kernels_02.cc  | 65 +++++++++++++++++
 .../hanging_node_kernels_02.output            |  2 +
 3 files changed, 137 insertions(+), 1 deletion(-)
 create mode 100644 tests/matrix_free/hanging_node_kernels_02.cc
 create mode 100644 tests/matrix_free/hanging_node_kernels_02.output

diff --git a/include/deal.II/matrix_free/hanging_nodes_internal.h b/include/deal.II/matrix_free/hanging_nodes_internal.h
index 7c5977b698..a34072e6d3 100644
--- a/include/deal.II/matrix_free/hanging_nodes_internal.h
+++ b/include/deal.II/matrix_free/hanging_nodes_internal.h
@@ -69,11 +69,26 @@ namespace internal
 
 
 
+    /**
+     * Type of the 9-bit representation of the refinement configuration.
+     */
+    using compressed_constraint_kind = std::uint8_t;
+
+
+
+    /**
+     * Value of compressed_constraint_kind for the unconstrained case.
+     */
+    constexpr compressed_constraint_kind
+      unconstrained_compressed_constraint_kind = 0;
+
+
+
     /**
      * Check if the combinations of the bits in @p kind_in are valid.
      */
     inline bool
-    check(const ConstraintKinds &kind_in, const unsigned int dim)
+    check(const ConstraintKinds kind_in, const unsigned int dim)
     {
       const std::uint16_t kind    = static_cast<std::uint16_t>(kind_in);
       const std::uint16_t subcell = (kind >> 0) & 7;
@@ -110,6 +125,60 @@ namespace internal
 
 
 
+    /**
+     * Compress a 9-bit representation of the refinement configuration
+     * to a 8-bit representation.
+     */
+    inline compressed_constraint_kind
+    compress(const ConstraintKinds kind_in, const unsigned int dim)
+    {
+      Assert(check(kind_in, dim), ExcInternalError());
+
+      if (dim == 2)
+        return static_cast<compressed_constraint_kind>(kind_in);
+
+      if (kind_in == ConstraintKinds::unconstrained)
+        return unconstrained_compressed_constraint_kind;
+
+      const std::uint16_t kind    = static_cast<std::uint16_t>(kind_in);
+      const std::uint16_t subcell = (kind >> 0) & 7;
+      const std::uint16_t face    = (kind >> 3) & 7;
+      const std::uint16_t edge    = (kind >> 6) & 7;
+
+      return subcell + ((face > 0) << 3) + ((edge > 0) << 4) +
+             (std::max(face, edge) << 5);
+    }
+
+
+
+    /**
+     * Decompress a 8-bit representation of the refinement configuration
+     * to a 9-bit representation.
+     */
+    inline ConstraintKinds
+    decompress(const compressed_constraint_kind kind_in, const unsigned int dim)
+    {
+      if (dim == 2)
+        return static_cast<ConstraintKinds>(kind_in);
+
+      if (kind_in == unconstrained_compressed_constraint_kind)
+        return ConstraintKinds::unconstrained;
+
+      const std::uint16_t subcell = (kind_in >> 0) & 7;
+      const std::uint16_t flag_0  = (kind_in >> 3) & 3;
+      const std::uint16_t flag_1  = (kind_in >> 5) & 7;
+
+      const auto result = static_cast<ConstraintKinds>(
+        subcell + (((flag_0 & 0b01) ? flag_1 : 0) << 3) +
+        (((flag_0 & 0b10) ? flag_1 : 0) << 6));
+
+      Assert(check(result, dim), ExcInternalError());
+
+      return result;
+    }
+
+
+
     /**
      * Return the memory consumption in bytes of this enum class.
      */
diff --git a/tests/matrix_free/hanging_node_kernels_02.cc b/tests/matrix_free/hanging_node_kernels_02.cc
new file mode 100644
index 0000000000..99110c961a
--- /dev/null
+++ b/tests/matrix_free/hanging_node_kernels_02.cc
@@ -0,0 +1,65 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2022 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// The deal.II library is free software; you can use it, redistribute
+// it, and/or modify it under the terms of the GNU Lesser General
+// Public License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+// The full text of the license can be found in the file LICENSE.md at
+// the top level directory of deal.II.
+//
+// ---------------------------------------------------------------------
+
+
+
+// Compress/decompress ConstraintKinds.
+
+#include <deal.II/dofs/dof_tools.h>
+
+#include <deal.II/fe/fe_q.h>
+
+#include <deal.II/grid/grid_generator.h>
+
+#include <deal.II/matrix_free/evaluation_kernels_hanging_nodes.h>
+#include <deal.II/matrix_free/fe_evaluation.h>
+#include <deal.II/matrix_free/matrix_free.h>
+
+#include <deal.II/numerics/vector_tools.h>
+
+#include "../tests.h"
+
+int
+main()
+{
+  initlog();
+
+  using namespace dealii::internal::MatrixFreeFunctions;
+
+  const unsigned int dim = 3;
+
+  const auto check = [&](const auto subcell, const auto face, const auto edge) {
+    const auto kind =
+      static_cast<ConstraintKinds>(subcell + (face << 3) + (edge << 6));
+
+    Assert(kind == decompress(compress(kind, dim), dim), ExcInternalError());
+  };
+
+  check(0, 0, 0);
+
+  for (unsigned int subcell = 0; subcell < 8; ++subcell)
+    {
+      for (unsigned int face = 1; face < 8; ++face)
+        check(subcell, face, 0);
+
+      for (unsigned int edge = 1; edge < 8; ++edge)
+        check(subcell, 0, edge);
+
+      for (unsigned int d = 0; d < dim; ++d)
+        check(subcell, 1 << d, 1 << d);
+    }
+
+  deallog << "OK!" << std::endl;
+}
diff --git a/tests/matrix_free/hanging_node_kernels_02.output b/tests/matrix_free/hanging_node_kernels_02.output
new file mode 100644
index 0000000000..5cfb783b8f
--- /dev/null
+++ b/tests/matrix_free/hanging_node_kernels_02.output
@@ -0,0 +1,2 @@
+
+DEAL::OK!
-- 
2.39.5