1 files changed, 42 insertions, 6 deletions

diff --git a/source/blender/blenlib/BLI_index_range.hh b/source/blender/blenlib/BLI_index_range.hh
index 7d5c2400bba..a0f129c7324 100644
--- a/source/blender/blenlib/BLI_index_range.hh
+++ b/source/blender/blenlib/BLI_index_range.hh
@@ -90,10 +90,10 @@ class IndexRange {
       return *this;
     }
 
-    constexpr Iterator operator++(int) const
+    constexpr Iterator operator++(int)
     {
       Iterator copied_iterator = *this;
-      ++copied_iterator;
+      ++(*this);
       return copied_iterator;
     }
 
@@ -186,13 +186,25 @@ class IndexRange {
   }
 
   /**
-   * Get the last element in the range.
-   * Asserts when the range is empty.
+   * Get the nth last element in the range.
+   * Asserts when the range is empty or when n is negative.
    */
-  constexpr int64_t last() const
+  constexpr int64_t last(const int64_t n = 0) const
   {
+    BLI_assert(n >= 0);
+    BLI_assert(n < size_);
     BLI_assert(this->size() > 0);
-    return start_ + size_ - 1;
+    return start_ + size_ - 1 - n;
+  }
+
+  /**
+   * Get the element one before the beginning. The returned value is undefined when the range is
+   * empty, and the range must start after zero already.
+   */
+  constexpr int64_t one_before_start() const
+  {
+    BLI_assert(start_ > 0);
+    return start_ - 1;
   }
 
   /**
@@ -280,6 +292,15 @@ class IndexRange {
   }
 
   /**
+   * Move the range forward or backward within the larger array. The amount may be negative,
+   * but its absolute value cannot be greater than the existing start of the range.
+   */
+  constexpr IndexRange shift(int64_t n) const
+  {
+    return IndexRange(start_ + n, size_);
+  }
+
+  /**
    * Get read-only access to a memory buffer that contains the range as actual numbers.
    */
   Span<int64_t> as_span() const;
@@ -297,4 +318,19 @@ class IndexRange {
   Span<int64_t> as_span_internal() const;
 };
 
+struct AlignedIndexRanges {
+  IndexRange prefix;
+  IndexRange aligned;
+  IndexRange suffix;
+};
+
+/**
+ * Split a range into three parts so that the boundaries of the middle part are aligned to some
+ * power of two.
+ *
+ * This can be used when an algorithm can be optimized on aligned indices/memory. The algorithm
+ * then needs a slow path for the beginning and end, and a fast path for the aligned elements.
+ */
+AlignedIndexRanges split_index_range_by_alignment(const IndexRange range, const int64_t alignment);
+
 }  // namespace blender