Refactor the hierarchy.

candle-core/src/strided_index.rs

@@ -0,0 +1,61 @@
+/// An iterator over offset position for items of an N-dimensional arrays stored in a
+/// flat buffer using some potential strides.
+#[derive(Debug)]
+pub(crate) struct StridedIndex<'a> {
+    next_storage_index: Option<usize>,
+    multi_index: Vec<usize>,
+    dims: &'a [usize],
+    stride: &'a [usize],
+}
+
+impl<'a> StridedIndex<'a> {
+    pub(crate) fn new(dims: &'a [usize], stride: &'a [usize]) -> Self {
+        let elem_count: usize = dims.iter().product();
+        let next_storage_index = if elem_count == 0 {
+            None
+        } else {
+            // This applies to the scalar case.
+            Some(0)
+        };
+        StridedIndex {
+            next_storage_index,
+            multi_index: vec![0; dims.len()],
+            dims,
+            stride,
+        }
+    }
+}
+
+impl<'a> Iterator for StridedIndex<'a> {
+    type Item = usize;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let storage_index = match self.next_storage_index {
+            None => return None,
+            Some(storage_index) => storage_index,
+        };
+        let mut updated = false;
+        for (multi_i, max_i) in self.multi_index.iter_mut().zip(self.dims.iter()).rev() {
+            let next_i = *multi_i + 1;
+            if next_i < *max_i {
+                *multi_i = next_i;
+                updated = true;
+                break;
+            } else {
+                *multi_i = 0
+            }
+        }
+        self.next_storage_index = if updated {
+            let next_storage_index = self
+                .multi_index
+                .iter()
+                .zip(self.stride.iter())
+                .map(|(&x, &y)| x * y)
+                .sum();
+            Some(next_storage_index)
+        } else {
+            None
+        };
+        Some(storage_index)
+    }
+}