Iteration over strided blocks (#175)

* Introduce the strided blocks.

* Use the strided blocks to fasten the copy.

* Add more testing.

candle-core/src/tensor.rs

@@ -834,10 +834,20 @@ impl Tensor {
         Ok(from_storage(storage, shape, op, false))
     }
 
-    pub(crate) fn strided_index(&self) -> crate::StridedIndex {
+    /// Returns an iterator over position of the elements in the storage when ranging over the
+    /// index tuples in lexicographic order.
+    pub fn strided_index(&self) -> crate::StridedIndex {
         self.layout.strided_index()
     }
 
+    /// Similar to `strided_index` but returns the position of the start of each contiguous block
+    /// as well as the length of the contiguous blocks. For a contiguous tensor, the index iterator
+    /// will only return the start offset and the size would be the number of elements in the
+    /// tensor.
+    pub fn strided_blocks(&self) -> crate::StridedBlocks {
+        self.layout.strided_blocks()
+    }
+
     /// Returns the data contained in a 1D tensor as a vector of scalar values.
     pub fn to_vec1<S: crate::WithDType>(&self) -> Result<Vec<S>> {
         if self.rank() != 1 {