test:Add power of 2 sharding indexing tests

Author: mkitti

tests/benchmarks/test_indexing.py

@@ -50,3 +50,45 @@ def test_slice_indexing(
 
     data[:] = 1
     benchmark(getitem, data, indexer)
+
+
+# Benchmark for Morton order optimization with power-of-2 shards
+# Morton order is used internally by sharding codec for chunk iteration
+morton_shards = (
+    (16,) * 3,  # With 2x2x2 chunks: 8x8x8 = 512 chunks per shard
+    (32,) * 3,  # With 2x2x2 chunks: 16x16x16 = 4096 chunks per shard
+)
+
+
+@pytest.mark.parametrize("store", ["memory"], indirect=["store"])
+@pytest.mark.parametrize("shards", morton_shards, ids=str)
+def test_sharded_morton_indexing(
+    store: Store,
+    shards: tuple[int, ...],
+    benchmark: BenchmarkFixture,
+) -> None:
+    """Benchmark sharded array indexing with power-of-2 chunks per shard.
+
+    This benchmark exercises the Morton order iteration path in the sharding
+    codec, which benefits from the hypercube and vectorization optimizations.
+    """
+    # Create array where each shard contains many small chunks
+    # e.g., shards=(32,32,32) with chunks=(2,2,2) means 16x16x16 = 4096 chunks per shard
+    shape = tuple(s * 2 for s in shards)  # 2 shards per dimension
+    chunks = (2,) * 3  # Small chunks to maximize chunks per shard
+
+    data = create_array(
+        store=store,
+        shape=shape,
+        dtype="uint8",
+        chunks=chunks,
+        shards=shards,
+        compressors=None,
+        filters=None,
+        fill_value=0,
+    )
+
+    data[:] = 1
+    # Read a sub-shard region to exercise Morton order iteration
+    indexer = (slice(shards[0]),) * 3
+    benchmark(getitem, data, indexer)