BUG: fix bug in dtype hash implementation for equivalent but different byte order character.

Author: cournape

numpy/core/src/multiarray/hashdescr.c

@@ -30,6 +30,23 @@ static int _array_descr_walk(PyArray_Descr* descr, PyObject *l);
 static int _array_descr_walk_fields(PyObject* fields, PyObject* l);
 static int _array_descr_builtin(PyArray_Descr* descr, PyObject *l);
 
+/*
+ * normalize endian character: always return 'I', '<' or '>'
+ */
+ static char _normalize_byteorder(char byteorder)
+ {
+	switch(byteorder) {
+	case '=':
+		if (PyArray_GetEndianness() == NPY_CPU_BIG) {
+			return '>';
+		} else {
+			return '<';
+		}
+	default:
+		return byteorder;
+	}
+ }
+
 /*
  * Return true if descr is a builtin type
  */
@@ -51,12 +68,13 @@ static int _array_descr_builtin(PyArray_Descr* descr, PyObject *l)
 {
     Py_ssize_t i;
     PyObject *t, *item;
+    char nbyteorder = _normalize_byteorder(descr->byteorder);
 
     /*
      * For builtin type, hash relies on : kind + byteorder + flags +
      * type_num + elsize + alignment
      */
-    t = Py_BuildValue("(cciiii)", descr->kind, descr->byteorder,
+    t = Py_BuildValue("(cciiii)", descr->kind, nbyteorder,
             descr->flags, descr->type_num, descr->elsize,
             descr->alignment);
 

numpy/core/tests/test_dtype.py

@@ -9,6 +9,19 @@ def test_run(self):
             dt = np.dtype(t)
             hash(dt)
 
+    def test_dtype(self):
+        # Make sure equivalent byte order char hash the same (e.g. < and = on
+        # little endian)
+        for t in [np.int, np.float]:
+            dt = np.dtype(t)
+            dt2 = dt.newbyteorder("<")
+            dt3 = dt.newbyteorder(">")
+            if dt == dt2:
+                self.assertTrue(dt.byteorder != dt2.byteorder, "bogus test")
+                self.assertTrue(hash(dt) == hash(dt2), "equivalent bytorders do not hash the same")
+            else:
+                self.assertTrue(dt.byteorder != dt3.byteorder, "bogus test")
+                self.assertTrue(hash(dt) == hash(dt3), "equivalent bytorders do not hash the same")
 class TestRecord(TestCase):
     def test_equivalent_record(self):
         """Test whether equivalent record dtypes hash the same."""