Support non-Hilbert decomposition

See ramses-organisation/ramses#72.

Author: cphyc

yt/frontends/ramses/data_structures.py

@@ -262,7 +262,14 @@ def _read_amr_header(self):
                 self._ngridbound = np.zeros(hvals["nlevelmax"], dtype="int64")
             _free_mem = f.read_attrs((("free_mem", 5, "i"),))
             _ordering = f.read_vector("c")
-            f.skip(4)
+            _ordering = "".join(_.decode() for _ in _ordering).strip()
+            if _ordering == "hilbert":
+                Nskip = 1  # bound_key
+            elif _ordering == "bisection":
+                Nskip = 5  #  bisec_wall, bisec_next, bisec_indx, bisec_cpubox_min, bisec_cpubox_max
+            else:
+                raise RuntimeError(f"Unknown ordering {_ordering!r} in AMR file")
+            f.skip(Nskip + 3)  # skip son, flag1, cpu_map
             # Now we're at the tree itself
             # Now we iterate over each level and each CPU.
             position = f.tell()