From 0668c68b031351488712f21290c77412b02c5de8 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Wed, 27 Jan 2021 23:29:33 +0100
Subject: Allow for negative strides.

Note that using a stride of -1 is still not possible because it would
clash with the definition of Eigen::Dynamic.

This fixes #747.
---
 test/mapstride.cpp | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

(limited to 'test/mapstride.cpp')

diff --git a/test/mapstride.cpp b/test/mapstride.cpp
index 09196600b..fde73f2ec 100644
--- a/test/mapstride.cpp
+++ b/test/mapstride.cpp
@@ -162,6 +162,32 @@ template<int Alignment,typename MatrixType> void map_class_matrix(const MatrixTy
     VERIFY_IS_APPROX(map,s1*m);
   }
 
+  // test negative strides
+  {
+    Matrix<Scalar,Dynamic,1>::Map(a_array1, arraysize+1).setRandom();
+    Index outerstride = m.innerSize()+4;
+    Scalar* array = array1;
+
+    {
+      Map<MatrixType, Alignment, OuterStride<> > map1(array, rows, cols, OuterStride<>( outerstride));
+      Map<MatrixType, Unaligned, OuterStride<> > map2(array+(m.outerSize()-1)*outerstride, rows, cols, OuterStride<>(-outerstride));
+      if(MatrixType::IsRowMajor)  VERIFY_IS_APPROX(map1.colwise().reverse(), map2);
+      else                        VERIFY_IS_APPROX(map1.rowwise().reverse(), map2);
+    }
+
+    {
+      Map<MatrixType, Alignment, OuterStride<> > map1(array, rows, cols, OuterStride<>( outerstride));
+      Map<MatrixType, Unaligned, Stride<Dynamic,Dynamic> > map2(array+(m.outerSize()-1)*outerstride+m.innerSize()-1, rows, cols, Stride<Dynamic,Dynamic>(-outerstride,-1));
+      VERIFY_IS_APPROX(map1.reverse(), map2);
+    }
+
+    {
+      Map<MatrixType, Alignment, OuterStride<> > map1(array, rows, cols, OuterStride<>( outerstride));
+      Map<MatrixType, Unaligned, Stride<Dynamic,-1> > map2(array+(m.outerSize()-1)*outerstride+m.innerSize()-1, rows, cols, Stride<Dynamic,-1>(-outerstride,-1));
+      VERIFY_IS_APPROX(map1.reverse(), map2);
+    }
+  }
+
   internal::aligned_delete(a_array1, arraysize+1);
 }
 
@@ -200,7 +226,7 @@ void bug1453()
 EIGEN_DECLARE_TEST(mapstride)
 {
   for(int i = 0; i < g_repeat; i++) {
-    int maxn = 30;
+    int maxn = 3;
     CALL_SUBTEST_1( map_class_vector<Aligned>(Matrix<float, 1, 1>()) );
     CALL_SUBTEST_1( map_class_vector<Unaligned>(Matrix<float, 1, 1>()) );
     CALL_SUBTEST_2( map_class_vector<Aligned>(Vector4d()) );
-- 
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