BLI: Add a reverse method to MutableSpan

Add a method that allows a MutableSpan to reverse itself. This reverses
the data in the original span object. This is a first step in extracting
some functionality from nodes and making it more general.

Differential Revision: https://developer.blender.org/D12485

2 files changed, 33 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_span.hh b/source/blender/blenlib/BLI_span.hh
index e04295b0e51..5adb47ba0b0 100644
--- a/source/blender/blenlib/BLI_span.hh
+++ b/source/blender/blenlib/BLI_span.hh
@@ -644,6 +644,16 @@ template<typename T> class MutableSpan {
   }
 
   /**
+   * Reverse the data in the MutableSpan.
+   */
+  constexpr void reverse()
+  {
+    for (const int i : IndexRange(size_ / 2)) {
+      std::swap(data_[size_ - 1 - i], data_[i]);
+    }
+  }
+
+  /**
    * Returns an (immutable) Span that references the same array. This is usually not needed,
    * due to implicit conversions. However, sometimes automatic type deduction needs some help.
    */
diff --git a/source/blender/blenlib/tests/BLI_span_test.cc b/source/blender/blenlib/tests/BLI_span_test.cc
index 4d23a53c08a..fb88fb63e53 100644
--- a/source/blender/blenlib/tests/BLI_span_test.cc
+++ b/source/blender/blenlib/tests/BLI_span_test.cc
@@ -362,6 +362,29 @@ TEST(span, ReverseIterator)
   EXPECT_EQ_ARRAY(reversed_vec.data(), Span({7, 6, 5, 4}).data(), 4);
 }
 
+TEST(span, ReverseMutableSpan)
+{
+  std::array<int, 0> src0 = {};
+  MutableSpan<int> span0 = src0;
+  span0.reverse();
+  EXPECT_EQ_ARRAY(span0.data(), Span<int>({}).data(), 0);
+
+  std::array<int, 1> src1 = {4};
+  MutableSpan<int> span1 = src1;
+  span1.reverse();
+  EXPECT_EQ_ARRAY(span1.data(), Span<int>({4}).data(), 1);
+
+  std::array<int, 2> src2 = {4, 5};
+  MutableSpan<int> span2 = src2;
+  span2.reverse();
+  EXPECT_EQ_ARRAY(span2.data(), Span<int>({5, 4}).data(), 2);
+
+  std::array<int, 5> src5 = {4, 5, 6, 7, 8};
+  MutableSpan<int> span5 = src5;
+  span5.reverse();
+  EXPECT_EQ_ARRAY(span5.data(), Span<int>({8, 7, 6, 5, 4}).data(), 5);
+}
+
 TEST(span, MutableReverseIterator)
 {
   std::array<int, 4> src = {4, 5, 6, 7};