Functions: Run-time type system and index mask

This adds a new `CPPType` that encapsulates information about how to handle
instances of a specific data type. This is necessary for the function evaluation
system, which will be used to evaluate most of the particle node trees.

Furthermore, this adds an `IndexMask` class which offers a surprisingly useful
abstraction over an array containing unsigned integers. It makes two assumptions
about the underlying integer array:
* The integers are in ascending order.
* There are no duplicates.

`IndexMask` will be used to "select" certain particles that will be
processed in a data-oriented way. Sometimes, operations don't have to
be applied to all particles, but only some, those that are in the indexed by
the `IndexMask`. The two limitations imposed by an `IndexMask` allow for
better performance.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D7957

1 files changed, 212 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_index_mask.hh b/source/blender/blenlib/BLI_index_mask.hh
new file mode 100644
index 00000000000..96ab8906bd4
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+++ b/source/blender/blenlib/BLI_index_mask.hh
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+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __BLI_INDEX_MASK_HH__
+#define __BLI_INDEX_MASK_HH__
+
+/** \file
+ * \ingroup bli
+ *
+ * An IndexMask references an array of unsigned integers with the following property:
+ *   The integers must be in ascending order and there must not be duplicates.
+ *
+ * Remember that the array is only referenced and not owned by an IndexMask instance.
+ *
+ * In most cases the integers in the array represent some indices into another array. So they
+ * "select" or "mask" a some elements in that array. Hence the name IndexMask.
+ *
+ * The invariant stated above has the nice property that it makes it easy to check if an integer
+ * array is an IndexRange, i.e. no indices are skipped. That allows functions to implement two code
+ * paths: One where it iterates over the index array and one where it iterates over the index
+ * range. The latter one is more efficient due to less memory reads and potential usage of SIMD
+ * instructions.
+ *
+ * The IndexMask.foreach_index method helps writing code that implements both code paths at the
+ * same time.
+ */
+
+#include "BLI_array_ref.hh"
+#include "BLI_index_range.hh"
+
+namespace BLI {
+
+class IndexMask {
+ private:
+  /* The underlying reference to sorted integers. */
+  ArrayRef<uint> m_indices;
+
+ public:
+  /* Creates an IndexMask that contains no indices. */
+  IndexMask() = default;
+
+  /**
+   * Create an IndexMask using the given integer array.
+   * This constructor asserts that the given integers are in ascending order and that there are no
+   * duplicates.
+   */
+  IndexMask(ArrayRef<uint> indices) : m_indices(indices)
+  {
+#ifdef DEBUG
+    for (uint i = 1; i < indices.size(); i++) {
+      BLI_assert(indices[i - 1] < indices[i]);
+    }
+#endif
+  }
+
+  /**
+   * Use this method when you know that no indices are skipped. It is more efficient than preparing
+   * an integer array all the time.
+   */
+  IndexMask(IndexRange range) : m_indices(range.as_array_ref())
+  {
+  }
+
+  /**
+   * Construct an IndexMask from a sorted list of indices. Note, the created IndexMask is only
+   * valid as long as the initializer_list is valid.
+   *
+   * Don't do this:
+   *   IndexMask mask = {3, 4, 5};
+   *
+   * Do this:
+   *   do_something_with_an_index_mask({3, 4, 5});
+   */
+  IndexMask(const std::initializer_list<uint> &indices) : IndexMask(ArrayRef<uint>(indices))
+  {
+  }
+
+  /**
+   * Creates an IndexMask that references the indices [0, n-1].
+   */
+  explicit IndexMask(uint n) : IndexMask(IndexRange(n))
+  {
+  }
+
+  operator ArrayRef<uint>() const
+  {
+    return m_indices;
+  }
+
+  const uint *begin() const
+  {
+    return m_indices.begin();
+  }
+
+  const uint *end() const
+  {
+    return m_indices.end();
+  }
+
+  /**
+   * Returns the n-th index referenced by this IndexMask. The `index_mask` method returns an
+   * IndexRange containing all indices that can be used as parameter here.
+   */
+  uint operator[](uint n) const
+  {
+    return m_indices[n];
+  }
+
+  /**
+   * Returns the minimum size an array has to have, if the integers in this IndexMask are going to
+   * be used as indices in that array.
+   */
+  uint min_array_size() const
+  {
+    if (m_indices.size() == 0) {
+      return 0;
+    }
+    else {
+      return m_indices.last() + 1;
+    }
+  }
+
+  ArrayRef<uint> indices() const
+  {
+    return m_indices;
+  }
+
+  /**
+   * Returns true if this IndexMask does not skip any indices. This check requires O(1) time.
+   */
+  bool is_range() const
+  {
+    return m_indices.size() > 0 && m_indices.last() - m_indices.first() == m_indices.size() - 1;
+  }
+
+  /**
+   * Returns the IndexRange referenced by this IndexMask. This method should only be called after
+   * the caller made sure that this IndexMask is actually a range.
+   */
+  IndexRange as_range() const
+  {
+    BLI_assert(this->is_range());
+    return IndexRange{m_indices.first(), m_indices.size()};
+  }
+
+  /**
+   * Calls the given callback for every referenced index. The callback has to take one unsigned
+   * integer as parameter.
+   *
+   * This method implements different code paths for the cases when the IndexMask represents a
+   * range or not.
+   */
+  template<typename CallbackT> void foreach_index(const CallbackT &callback) const
+  {
+    if (this->is_range()) {
+      IndexRange range = this->as_range();
+      for (uint i : range) {
+        callback(i);
+      }
+    }
+    else {
+      for (uint i : m_indices) {
+        callback(i);
+      }
+    }
+  }
+
+  /**
+   * Returns an IndexRange that can be used to index this IndexMask.
+   *
+   * The range is [0, number of indices - 1].
+   *
+   * This is not to be confused with the `as_range` method.
+   */
+  IndexRange index_range() const
+  {
+    return m_indices.index_range();
+  }
+
+  /**
+   * Returns the largest index that is referenced by this IndexMask.
+   */
+  uint last() const
+  {
+    return m_indices.last();
+  }
+
+  /**
+   * Returns the number of indices referenced by this IndexMask.
+   */
+  uint size() const
+  {
+    return m_indices.size();
+  }
+};
+
+}  // namespace BLI
+
+#endif /* __BLI_INDEX_MASK_HH__ */