From 9110e55d9eac43803bc9af95e7bd44ecde916e4f Mon Sep 17 00:00:00 2001
From: "Kacper Kowalik (Xarthisius)" <xarthisius.kk@gmail.com>
Date: Sat, 31 Oct 2020 18:30:45 -0500
Subject: [PATCH 1/3] Fix expected values in the original BE test.

Add a new simple test.
---
 h5py/tests/test_big_endian_file.py | 44 ++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 14 deletions(-)

diff --git a/h5py/tests/test_big_endian_file.py b/h5py/tests/test_big_endian_file.py
index 7af322ff3..83fb92aa9 100644
--- a/h5py/tests/test_big_endian_file.py
+++ b/h5py/tests/test_big_endian_file.py
@@ -1,34 +1,50 @@
 import pytest
 
+import numpy as np
 from h5py import File
+from .common import TestCase
 from .data_files import get_data_file_path
 
 
 def test_vlen_big_endian():
     with File(get_data_file_path("vlen_string_s390x.h5")) as f:
-        assert f.attrs['created_on_s390x'] == 1
+        assert f.attrs["created_on_s390x"] == 1
 
-        dset = f['DSvariable']
-        assert dset[0] == b'Parting'
-        assert dset[1] == b'is such'
-        assert dset[2] == b'sweet'
-        assert dset[3] == b'sorrow...'
+        dset = f["DSvariable"]
+        assert dset[0] == b"Parting"
+        assert dset[1] == b"is such"
+        assert dset[2] == b"sweet"
+        assert dset[3] == b"sorrow..."
 
-        dset = f['DSLEfloat']
+        dset = f["DSLEfloat"]
         assert dset[0] == 3.14
         assert dset[1] == 1.61
         assert dset[2] == 2.71
         assert dset[3] == 2.41
         assert dset[4] == 1.2
-        assert dset.dtype == '<f8'
+        assert dset.dtype == "<f8"
 
         # Same float values with big endianess
-        assert f['DSBEfloat'][0] == pytest.approx(7.9824696849641e-157)
-        assert f['DSBEfloat'].dtype == '>f8'
+        assert f["DSBEfloat"][0] == 3.14
+        assert f["DSBEfloat"].dtype == ">f8"
 
-        assert f['DSLEint'][0] == 1
-        assert f['DSLEint'].dtype == 'uint64'
+        assert f["DSLEint"][0] == 1
+        assert f["DSLEint"].dtype == "uint64"
 
         # Same int values with big endianess
-        assert f['DSBEint'][0] == 72057594037927936
-        assert f['DSBEint'].dtype == '>i8'
+        assert f["DSBEint"][0] == 1
+        assert f["DSBEint"].dtype == ">i8"
+
+
+class TestEndianess(TestCase):
+    def test_simple_int_be(self):
+        fname = self.mktemp()
+
+        arr = np.ndarray(shape=(1,), dtype=">i4", buffer=bytearray([0, 1, 3, 2]))
+        be_number = 0 * 256 ** 3 + 1 * 256 ** 2 + 3 * 256 ** 1 + 2 * 256 ** 0
+
+        with File(fname, mode="w") as f:
+            f.create_dataset("int", data=arr)
+
+        with File(fname, mode="r") as f:
+            assert f["int"][()][0] == be_number

From a8cd2cbfbd3e7b45bc1c127360c2ee7e64ae85b3 Mon Sep 17 00:00:00 2001
From: "Kacper Kowalik (Xarthisius)" <xarthisius.kk@gmail.com>
Date: Sat, 31 Oct 2020 18:34:25 -0500
Subject: [PATCH 2/3] Preserve the endianess in Reader. Fixes #1729

---
 h5py/_selector.pyx | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/h5py/_selector.pyx b/h5py/_selector.pyx
index 1b06e75e6..9b19a4210 100644
--- a/h5py/_selector.pyx
+++ b/h5py/_selector.pyx
@@ -19,6 +19,8 @@ from .h5s cimport SpaceID
 from .h5t cimport TypeID, typewrap, py_create
 from .utils cimport emalloc, efree, convert_dims
 
+import sys
+
 import_array()
 
 
@@ -293,6 +295,7 @@ cdef class Reader:
     cdef Selector selector
     cdef TypeID h5_memory_datatype
     cdef int np_typenum
+    cdef char np_byteorder
 
     def __cinit__(self, DatasetID dsid):
         self.dataset = dsid.id
@@ -305,6 +308,7 @@ cdef class Reader:
         h5_stored_datatype = typewrap(H5Dget_type(self.dataset))
         np_dtype = h5_stored_datatype.py_dtype()
         self.np_typenum = np_dtype.num
+        self.np_byteorder = np_dtype.byteorder
         self.h5_memory_datatype = py_create(np_dtype)
 
     cdef ndarray make_array(self, hsize_t* mshape):
@@ -325,6 +329,8 @@ cdef class Reader:
                     arr_rank += 1
 
             arr = PyArray_SimpleNew(arr_rank, arr_shape, self.np_typenum)
+            if self.np_byteorder == (sys.byteorder == 'little' and '>' or '<'):
+                arr = arr.byteswap().newbyteorder()
         finally:
             efree(arr_shape)
 

From a79e616a6cdcae55b82046b7461b90fbda393ee0 Mon Sep 17 00:00:00 2001
From: "Kacper Kowalik (Xarthisius)" <xarthisius.kk@gmail.com>
Date: Sat, 31 Oct 2020 18:50:24 -0500
Subject: [PATCH 3/3] Add info about bugfix in news and update .authors

---
 .authors.yml             | 7 +++++++
 news/fix_be_fastread.rst | 4 ++++
 2 files changed, 11 insertions(+)
 create mode 100644 news/fix_be_fastread.rst

diff --git a/.authors.yml b/.authors.yml
index 927b9f2d7..38aca6fcd 100644
--- a/.authors.yml
+++ b/.authors.yml
@@ -828,3 +828,10 @@
   num_commits: 2
   first_commit: 2020-10-13 03:57:42
   github: opoplawski
+- name: Kacper Kowalik
+  email: xarthisius.kk@gmail.com
+  aliases:
+    - Kacper Kowalik (Xarthisius)
+  num_commit: 2
+  first_commit: 2020-10-31 18:30:45
+  github: Xarthisius
diff --git a/news/fix_be_fastread.rst b/news/fix_be_fastread.rst
new file mode 100644
index 000000000..64dfc41e2
--- /dev/null
+++ b/news/fix_be_fastread.rst
@@ -0,0 +1,4 @@
+Bug fixes
+---------
+
+* Preserve endianess in Cython dataset Reader (:issue:`1729`).