BUG: Don't call float when constructing longdouble arrays

This addresses some of #8902, preventing precision loss

2 files changed, 43 insertions, 0 deletions

diff --git a/numpy/core/src/multiarray/arraytypes.c.src b/numpy/core/src/multiarray/arraytypes.c.src
index b43f267f3..1fa54d325 100644
--- a/numpy/core/src/multiarray/arraytypes.c.src
+++ b/numpy/core/src/multiarray/arraytypes.c.src
@@ -374,6 +374,20 @@ LONGDOUBLE_setitem(PyObject *op, void *ov, void *vap)
     /* ensure alignment */
     npy_longdouble temp;
 
+    /* Handle case of assigning from an array scalar */
+    if (PyArray_Check(op) && PyArray_NDIM((PyArrayObject *)op) == 0) {
+        PyObject *temp = PyArray_ToScalar(PyArray_BYTES((PyArrayObject *)op),
+                                          (PyArrayObject *)op);
+        if (temp == NULL) {
+            return -1;
+        }
+        else {
+            int res = LONGDOUBLE_setitem(temp, ov, ap);
+            Py_DECREF(temp);
+            return res;
+        }
+    }
+
     if (PyArray_IsScalar(op, LongDouble)) {
         temp = ((PyLongDoubleScalarObject *)op)->obval;
     }
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index f7cb58bc1..373f151b2 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -404,6 +404,35 @@ class TestAssignment(TestCase):
         # this would crash for the same reason
         np.array([np.array(u'\xe5\xe4\xf6')])
 
+    def test_longdouble_assignment(self):
+        # only relevant if longdouble is larger than float
+        # we're looking for loss of precision
+
+        # gh-8902
+        tinyb = np.nextafter(np.longdouble(0), 1)
+        tinya =  np.nextafter(np.longdouble(0), -1)
+        tiny1d = np.array([tinya])
+        assert_equal(tiny1d[0], tinya)
+
+        # scalar = scalar
+        tiny1d[0] = tinyb
+        assert_equal(tiny1d[0], tinyb)
+
+        # 0d = scalar
+        tiny1d[0, ...] = tinya
+        assert_equal(tiny1d[0], tinya)
+
+        # 0d = 0d
+        tiny1d[0, ...] = tinyb[...]
+        assert_equal(tiny1d[0], tinyb)
+
+        # scalar = 0d
+        tiny1d[0] = tinyb[...]
+        assert_equal(tiny1d[0], tinyb)
+
+        arr = np.array([np.array(tinya)])
+        assert_equal(arr[0], tinya)
+
 
 class TestDtypedescr(TestCase):
     def test_construction(self):