Issue #1575020: Fixed support of 24-bit wave files on big-endian platforms.

3 files changed, 14 insertions, 5 deletions

diff --git a/Lib/test/test_wave.py b/Lib/test/test_wave.py
index b4413c6..cf069ae 100644
--- a/Lib/test/test_wave.py
+++ b/Lib/test/test_wave.py
@@ -49,9 +49,6 @@ class WavePCM16Test(audiotests.AudioWriteTests,
         frames = audiotests.byteswap2(frames)
 
 
-@unittest.skipIf(sys.byteorder == 'big',
-                 '24-bit wave files are supported only on little-endian '
-                 'platforms')
 class WavePCM24Test(audiotests.AudioWriteTests,
         audiotests.AudioTestsWithSourceFile,
         unittest.TestCase):
diff --git a/Lib/wave.py b/Lib/wave.py
index 0e6628b..e723423 100644
--- a/Lib/wave.py
+++ b/Lib/wave.py
@@ -87,6 +87,12 @@ import sys
 from chunk import Chunk
 from collections import namedtuple
 
+def _byteswap3(data):
+    ba = bytearray(data)
+    ba[::3] = data[2::3]
+    ba[2::3] = data[::3]
+    return bytes(ba)
+
 _wave_params = namedtuple('_wave_params',
                      'nchannels sampwidth framerate nframes comptype compname')
 
@@ -237,7 +243,7 @@ class Wave_read:
             self._data_seek_needed = 0
         if nframes == 0:
             return b''
-        if self._sampwidth > 1 and sys.byteorder == 'big':
+        if self._sampwidth in (2, 4) and sys.byteorder == 'big':
             # unfortunately the fromfile() method does not take
             # something that only looks like a file object, so
             # we have to reach into the innards of the chunk object
@@ -258,6 +264,8 @@ class Wave_read:
             data = data.tobytes()
         else:
             data = self._data_chunk.read(nframes * self._framesize)
+            if self._sampwidth == 3 and sys.byteorder == 'big':
+                data = _byteswap3(data)
         if self._convert and data:
             data = self._convert(data)
         self._soundpos = self._soundpos + len(data) // (self._nchannels * self._sampwidth)
@@ -431,7 +439,7 @@ class Wave_write:
         nframes = len(data) // (self._sampwidth * self._nchannels)
         if self._convert:
             data = self._convert(data)
-        if self._sampwidth > 1 and sys.byteorder == 'big':
+        if self._sampwidth in (2, 4) and sys.byteorder == 'big':
             import array
             data = array.array(_array_fmts[self._sampwidth], data)
             assert data.itemsize == self._sampwidth
@@ -439,6 +447,8 @@ class Wave_write:
             data.tofile(self._file)
             self._datawritten = self._datawritten + len(data) * self._sampwidth
         else:
+            if self._sampwidth == 3 and sys.byteorder == 'big':
+                data = _byteswap3(data)
             self._file.write(data)
             self._datawritten = self._datawritten + len(data)
         self._nframeswritten = self._nframeswritten + nframes
diff --git a/Misc/NEWS b/Misc/NEWS
index 107d084..e780fdf 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -34,6 +34,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #1575020: Fixed support of 24-bit wave files on big-endian platforms.
+
 - Issue #19378: Fixed a number of cases in the dis module where the new
   "file" parameter was not being honoured correctly