Merge pull request #1095 from efiring/colormap_byteorder_bug

Colormap byteorder bug

lib/matplotlib/__init__.py

@@ -1008,6 +1008,7 @@ def tk_window_focus():
     'matplotlib.tests.test_basic',
     'matplotlib.tests.test_cbook',
     'matplotlib.tests.test_colorbar',
+    'matplotlib.tests.test_colors',
     'matplotlib.tests.test_dates',
     'matplotlib.tests.test_delaunay',
     'matplotlib.tests.test_figure',

lib/matplotlib/colors.py

@@ -515,10 +515,17 @@ def __call__(self, X, alpha=None, bytes=False):
             xa = xma.filled()             # Fill to avoid infs, etc.
             del xma
 
-        if xa.dtype.char in np.typecodes['Float']:
+        # Calculations with native byteorder are faster, and avoid a
+        # bug that otherwise can occur with putmask when the last
+        # argument is a numpy scalar.
+        if not xa.dtype.isnative:
+            xa = xa.byteswap().newbyteorder()
+
+        if xa.dtype.kind == "f":
             # Treat 1.0 as slightly less than 1.
-            cbook._putmask(xa, xa==1.0, np.nextafter(xa.dtype.type(1),
-                                                     xa.dtype.type(0)))
+            vals = np.array([1, 0], dtype=xa.dtype)
+            almost_one = np.nextafter(*vals)
+            cbook._putmask(xa, xa==1.0, almost_one)
             # The following clip is fast, and prevents possible
             # conversion of large positive values to negative integers.
 

lib/matplotlib/tests/test_colors.py

@@ -0,0 +1,26 @@
+"""
+Tests for the colors module.
+"""
+
+from __future__ import print_function
+import numpy as np
+from numpy.testing.utils import assert_array_equal
+import matplotlib.colors as mcolors
+import matplotlib.cm as cm
+
+def test_colormap_endian():
+    """
+    Github issue #1005: a bug in putmask caused erroneous
+    mapping of 1.0 when input from a non-native-byteorder
+    array.
+    """
+    cmap = cm.get_cmap("jet")
+    # Test under, over, and invalid along with values 0 and 1.
+    a = [-0.5, 0, 0.5, 1, 1.5, np.nan]
+    for dt in ["f2", "f4", "f8"]:
+        anative = np.ma.masked_invalid(np.array(a, dtype=dt))
+        aforeign = anative.byteswap().newbyteorder()
+        #print(anative.dtype.isnative, aforeign.dtype.isnative)
+        assert_array_equal(cmap(anative), cmap(aforeign))
+
+