test and fix stride/dim overlap check

Author: vbarrielle

src/dimension.rs

@@ -47,13 +47,13 @@ pub fn dim_stride_overlap<D: Dimension>(dim: &D, strides: &D) -> bool
 {
     let order = fastest_varying_order(strides);
 
-    let mut sum = 0;
+    let mut prev_offset = 1;
     for &ind in order.slice().iter() {
         let s = strides.slice()[ind];
-        if (s as isize) < sum {
+        if (s as isize) < prev_offset {
             return true;
         }
-        sum += stride_offset(dim.slice()[ind], s);
+        prev_offset = stride_offset(dim.slice()[ind], s);
     }
     false
 }

src/lib.rs

@@ -75,7 +75,12 @@ use std::marker::PhantomData;
 
 use it::ZipSlices;
 
-pub use dimension::{Dimension, RemoveAxis, can_index_slice};
+pub use dimension::{
+    Dimension,
+    RemoveAxis,
+    can_index_slice,
+    dim_stride_overlap,
+};
 pub use dimension::NdIndex;
 pub use indexes::Indexes;
 pub use shape_error::ShapeError;

tests/dimension.rs

@@ -4,7 +4,8 @@ use ndarray::{
     Array,
     RemoveAxis,
     arr2,
-    can_index_slice
+    can_index_slice,
+    dim_stride_overlap,
 };
 
 #[test]
@@ -48,3 +49,13 @@ fn slice_indexing_uncommon_strides()
     let strides = (2, 4, 12);
     assert!(!can_index_slice(&v, &dim, &strides));
 }
+
+#[test]
+fn overlapping_strides_dim()
+{
+    let dim = (2, 3, 2);
+    let strides = (5, 2, 1);
+    assert!(dim_stride_overlap(&dim, &strides));
+    let strides = (6, 2, 1);
+    assert!(!dim_stride_overlap(&dim, &strides));
+}