[InMemoryDataset redesign] Object-oriented as_subchunk_map

versioned_hdf5/meson.build

@@ -51,6 +51,9 @@ cython_args = [
 
 py.extension_module(
     'hyperspace',
+    # FIXME This is a symlink. Can't find a way to convince Meson to compile
+    # with Cython pure-python .py files
+    # (read: https://cython.readthedocs.io/en/latest/src/tutorial/pure.html)
     'hyperspace.pyx',
     install: true,
     subdir: 'versioned_hdf5',
@@ -59,10 +62,8 @@ py.extension_module(
 
 py.extension_module(
     'subchunk_map',
-    # FIXME This is a symlink. Can't find a way to convince Meson to compile
-    # with Cython pure-python .py files
-    # (read: https://cython.readthedocs.io/en/latest/src/tutorial/pure.html)
     'subchunk_map.pyx',
     install: true,
     subdir: 'versioned_hdf5',
+    cython_args: cython_args,
 )

versioned_hdf5/subchunk_map.pxd

@@ -0,0 +1,25 @@
+# This file allows cimport'ing the functions declared below from other Cython modules
+
+from cython cimport Py_ssize_t
+
+
+cdef class IndexChunkMapper:
+    cdef readonly Py_ssize_t[:] chunk_indices
+    cdef readonly Py_ssize_t chunk_size
+    cdef readonly Py_ssize_t dset_size
+
+    cpdef tuple[object, object] chunk_submap(
+        self,
+        Py_ssize_t chunk_start_idx,
+        Py_ssize_t chunk_stop_idx,
+        bint shift,
+    )
+
+    # Private methods. Cython complains if we don't export _everything_.
+    cdef tuple[Py_ssize_t, Py_ssize_t] _chunk_start_stop(
+        self, Py_ssize_t a, Py_ssize_t b
+    )
+    cdef tuple[object, object, object] chunk_submap_compat(self, Py_ssize_t chunk_idx)
+
+# Utility functions
+cpdef Py_ssize_t ceil_a_over_b(Py_ssize_t a, Py_ssize_t b)