Force little-endian format when writing eeg datafile (#80)

* force little-endian format when writing eeg datafile Fix styling guideline * add information regarding little-endian format in the docs * tweak readme text * modify condition when to swap bytes * fit if clause on one line Co-authored-by: Clemens Brunner <[email protected]> * Ignore lines that cannot be tested from coverage * Update contributors list and changelog * remove redundant comments/pragmas * add website and fix naming syntax * Update docs/changelog.rst Co-authored-by: Clemens Brunner <[email protected]> * Fix indentation error E129 * Apply suggestions from code review * simplify check * changelog style Co-authored-by: Stefan Appelhoff <[email protected]> Co-authored-by: Clemens Brunner <[email protected]>
bids-standard · Sep 29, 2021 · 0088662 · 0088662
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diff --git a/CITATION.cff b/CITATION.cff
@@ -23,6 +23,9 @@ authors:
 - given-names: "Phillip"
   family-names: "Alday"
   orcid: https://orcid.org/0000-0002-9984-5745
+- given-names: "Aniket"
+  family-names: "Pradhan"
+  orcid: https://orcid.org/0000-0002-6705-5116
 title: "pybv"
 version: 0.5.0
 date-released: 2021-01-03

diff --git a/README.rst b/README.rst
@@ -60,7 +60,12 @@ consisting of:
 - comments marked as ``; comment``
 - key-value pairs marked as ``key=value``
 
-A documentation for core BrainVision file format is provided by Brain Products.
+The binary ``.eeg`` data file is written in little-endian format without a Byte Order
+Mark (BOM), in accordance with the specification by Brain Products.
+This ensures that the data file is uniformly written irrespective of the
+native system architecture.
+
+A documentation for the BrainVision file format is provided by Brain Products.
 You can `view the specification <https://www.brainproducts.com/productdetails.php?id=21&tab=5>`_
 as hosted by Brain Products.
 

diff --git a/docs/changelog.rst b/docs/changelog.rst
@@ -7,6 +7,7 @@ Authors
 People who contributed to this software across releases (in **alphabetical order**):
 
 - `Adam Li`_
+- `Aniket Pradhan`_
 - `Chris Holdgraf`_
 - `Clemens Brunner`_
 - `Phillip Alday`_
@@ -31,13 +32,16 @@ Current (unreleased)
 
 Changelog
 ~~~~~~~~~
-
 - :func:`pybv.write_brainvision` gained a new parameter, ``ref_ch_names``, to specify the reference channels used during recording, by `Richard Höchenberger`_ and `Stefan Appelhoff`_ (:gh:`75`)
 
 API
 ~~~
 - :func:`pybv.write_brainvision` now has an ``overwrite`` parameter that defaults to ``False``, by `Stefan Appelhoff`_ (:gh:`78`).
 
+Bug
+~~~
+- Fix bug where :func:`pybv.write_brainvision` would write the binary file in big-endian on a big-endian system, by `Aniket Pradhan`_, `Clemens Brunner`_, and `Stefan Appelhoff`_ (:gh:`80`)
+
 0.5.0 (2021-01-03)
 ==================
 
@@ -125,3 +129,4 @@ Changelog
 .. _Clemens Brunner: https://cbrnr.github.io/
 .. _Richard Höchenberger: https://hoechenberger.net/
 .. _Adam Li: https://adam2392.github.io/
+.. _Aniket Pradhan: http://home.iiitd.edu.in/~aniket17133/
diff --git a/pybv/io.py b/pybv/io.py
@@ -14,6 +14,7 @@
 import datetime
 import os
 import shutil
+import sys
 from os import path as op
 from warnings import warn
 
@@ -491,5 +492,14 @@ def _write_bveeg_file(eeg_fname, data, orientation, format, resolution, units):
         raise ValueError(msg)
     data = data.astype(dtype=dtype)
 
+    # We always write data as little-endian without BOM
+    # `data` is already in native byte order due to numpy operations that
+    # result in copies of the `data` array (see above)
+    assert data.dtype.byteorder == "="
+
+    # swap bytes if system architecture is big-endian
+    if sys.byteorder == "big":  # pragma: no cover
+        data = data.byteswap()
+
     # Save to binary
     data.ravel(order='F').tofile(eeg_fname)