Merge pull request #14669 from siddhesh/undefined-float2datetime

BUG: Do not rely on undefined behaviour to cast from float to datetime

2 files changed, 44 insertions, 2 deletions

diff --git a/numpy/core/src/multiarray/arraytypes.c.src b/numpy/core/src/multiarray/arraytypes.c.src
index 152a2be9c..a82ad7935 100644
--- a/numpy/core/src/multiarray/arraytypes.c.src
+++ b/numpy/core/src/multiarray/arraytypes.c.src
@@ -1081,6 +1081,7 @@ TIMEDELTA_setitem(PyObject *op, void *ov, void *vap)
  *           npy_long, npy_ulong, npy_longlong, npy_ulonglong,
  *           npy_float, npy_double, npy_longdouble,
  *           npy_datetime, npy_timedelta#
+ * #supports_nat = 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1#
  */
 
 /**begin repeat1
@@ -1092,6 +1093,7 @@ TIMEDELTA_setitem(PyObject *op, void *ov, void *vap)
  *             npy_long, npy_ulong, npy_longlong, npy_ulonglong,
  *             npy_float, npy_double, npy_longdouble,
  *             npy_datetime, npy_timedelta#
+ * #floatingpoint = 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0#
  */
 static void
 @FROMTYPE@_to_@TOTYPE@(void *input, void *output, npy_intp n,
@@ -1101,7 +1103,15 @@ static void
     @totype@ *op = output;
 
     while (n--) {
-        *op++ = (@totype@)*ip++;
+        @fromtype@ f = *ip++;
+        @totype@ t = (@totype@)f;
+#if @supports_nat@ && @floatingpoint@
+        /* Avoid undefined behaviour for NaN -> NaT */
+        if (npy_isnan(f)) {
+            t = (@totype@)NPY_DATETIME_NAT;
+        }
+#endif
+        *op++ = t;
     }
 }
 /**end repeat1**/
@@ -1119,7 +1129,15 @@ static void
     @totype@ *op = output;
 
     while (n--) {
-        *op++ = (@totype@)*ip;
+        @fromtype@ f = *ip;
+        @totype@ t = (@totype@)f;
+#if @supports_nat@
+        /* Avoid undefined behaviour for NaN -> NaT */
+        if (npy_isnan(f)) {
+            t = (@totype@)NPY_DATETIME_NAT;
+        }
+#endif
+        *op++ = t;
         ip += 2;
     }
 }
diff --git a/numpy/core/tests/test_datetime.py b/numpy/core/tests/test_datetime.py
index 11f900c5f..a756dc7e7 100644
--- a/numpy/core/tests/test_datetime.py
+++ b/numpy/core/tests/test_datetime.py
@@ -483,6 +483,30 @@ class TestDateTime(object):
         assert_equal(np.datetime64(a, '[Y]'), np.datetime64('NaT', '[Y]'))
         assert_equal(np.datetime64(a, '[W]'), np.datetime64('NaT', '[W]'))
 
+        # NaN -> NaT
+        nan = np.array([np.nan] * 8)
+        fnan = nan.astype('f')
+        lnan = nan.astype('g')
+        cnan = nan.astype('D')
+        cfnan = nan.astype('F')
+        clnan = nan.astype('G')
+
+        nat = np.array([np.datetime64('NaT')] * 8)
+        assert_equal(nan.astype('M8[ns]'), nat)
+        assert_equal(fnan.astype('M8[ns]'), nat)
+        assert_equal(lnan.astype('M8[ns]'), nat)
+        assert_equal(cnan.astype('M8[ns]'), nat)
+        assert_equal(cfnan.astype('M8[ns]'), nat)
+        assert_equal(clnan.astype('M8[ns]'), nat)
+
+        nat = np.array([np.timedelta64('NaT')] * 8)
+        assert_equal(nan.astype('timedelta64[ns]'), nat)
+        assert_equal(fnan.astype('timedelta64[ns]'), nat)
+        assert_equal(lnan.astype('timedelta64[ns]'), nat)
+        assert_equal(cnan.astype('timedelta64[ns]'), nat)
+        assert_equal(cfnan.astype('timedelta64[ns]'), nat)
+        assert_equal(clnan.astype('timedelta64[ns]'), nat)
+
     def test_days_creation(self):
         assert_equal(np.array('1599', dtype='M8[D]').astype('i8'),
                 (1600-1970)*365 - (1972-1600)/4 + 3 - 365)