On-the-fly endianness conversion (#125)

* On-the-fly byte-swapping

* Upd changes

* linting

* Remove on-the-fly byte-swap, switch to scipy instead

CHANGES.rst

@@ -6,10 +6,10 @@ What's new
 
 Bug fixes
 ~~~~~~~~~
+- The introduction of `sparse`, with `numba` under the hood, restricted input data to little-endian dtypes. In those cases, xESMF switches back to using scipy (:pull:`125`). By `Pascal Bourgault <https://github.com/aulemahal>`_
 - Regridding datasets with dask-backed variables is fixed. Dtype of the outputs is changed for this specific case. By `Pascal Bourgault <https://github.com/aulemahal>`_
 - SpatialAverager did not compute the same weights as Regridder when source cell areas were not uniform (:pull:`128`). By `David Huard <https://github.com/huard>`_
 
-
 0.6.1 (23-09-2021)
 ------------------
 

setup.cfg

@@ -8,7 +8,7 @@ extend-ignore = E203,E501,E402,W605
 
 [isort]
 known_first_party=xesmf
-known_third_party=ESMF,cf_xarray,cftime,dask,numpy,pytest,setuptools,shapely,sparse,xarray
+known_third_party=ESMF,cf_xarray,cftime,dask,numba,numpy,pytest,setuptools,shapely,sparse,xarray
 multi_line_output=3
 include_trailing_comma=True
 force_grid_wrap=0

xesmf/smm.py

@@ -5,6 +5,7 @@
 import warnings
 from pathlib import Path
 
+import numba as nb
 import numpy as np
 import sparse as sps
 import xarray as xr
@@ -120,6 +121,15 @@ def apply_weights(weights, indata, shape_in, shape_out):
         Extra dimensions are the same as `indata`.
         If input data is C-ordered, output will also be C-ordered.
     """
+    # Limitation from numba : some big-endian dtypes are not supported.
+    try:
+        nb.from_dtype(indata.dtype)
+        nb.from_dtype(weights.dtype)
+    except NotImplementedError:
+        warnings.warn(
+            'Input array has a dtype not supported by sparse and numba. Falling back to scipy.'
+        )
+        weights = weights.to_scipy_sparse()
 
     # COO matrix is fast with F-ordered array but slow with C-array, so we
     # take in a C-ordered and then transpose)

xesmf/tests/test_frontend.py

@@ -411,6 +411,19 @@ def test_regrid_dataarray(use_cfxr):
         xr.testing.assert_identical(dr_out, dr_out_rn)
 
 
+def test_regrid_dataarray_endianess():
+    # xarray.DataArray containing in-memory numpy array
+    regridder = xe.Regridder(ds_in, ds_out, 'conservative')
+
+    exp = regridder(ds_in['data'])  # Normal (little-endian)
+    with pytest.warns(UserWarning, match='Input array has a dtype not supported'):
+        out = regridder(ds_in['data'].astype('>f8'))  # big endian
+
+    # Results should be the same
+    assert_equal(exp.values, out.values)
+    assert out.dtype == '>f8'
+
+
 def test_regrid_dataarray_to_locstream():
     # xarray.DataArray containing in-memory numpy array