numpy · mattip · Nov 7, 2019 · Nov 7, 2019
diff --git a/numpy/random/_mt19937.pyx b/numpy/random/_mt19937.pyx
@@ -129,9 +129,9 @@ cdef class MT19937(BitGenerator):
         BitGenerator.__init__(self, seed)
         val = self._seed_seq.generate_state(RK_STATE_LEN, np.uint32)
         # MSB is 1; assuring non-zero initial array
-        self.rng_state.key[0] = 0x80000000UL
-        for i in range(1, RK_STATE_LEN):
+        for i in range(RK_STATE_LEN):
             self.rng_state.key[i] = val[i]
+        self.rng_state.key[0] |= 0x80000000UL
         self.rng_state.pos = i
 
         self._bitgen.state = &self.rng_state
@@ -169,9 +169,9 @@ cdef class MT19937(BitGenerator):
                     seed = SeedSequence()
                     val = seed.generate_state(RK_STATE_LEN)
                     # MSB is 1; assuring non-zero initial array
-                    self.rng_state.key[0] = 0x80000000UL
-                    for i in range(1, RK_STATE_LEN):
+                    for i in range(RK_STATE_LEN):
                         self.rng_state.key[i] = val[i]
+                    self.rng_state.key[0] |= 0x80000000UL
                 else:
                     if hasattr(seed, 'squeeze'):
                         seed = seed.squeeze()

diff --git a/numpy/random/src/mt19937/mt19937.c b/numpy/random/src/mt19937/mt19937.c
@@ -77,7 +77,7 @@ void mt19937_init_by_array(mt19937_state *state, uint32_t *init_key,
     }
   }
 
-  mt[0] = 0x80000000UL; /* MSB is 1; assuring non-zero initial array */
+  mt[0] |= 0x80000000UL; /* MSB is 1; assuring non-zero initial array */
 }
 
 void mt19937_gen(mt19937_state *state) {

diff --git a/numpy/random/tests/test_generator_mt19937.py b/numpy/random/tests/test_generator_mt19937.py
@@ -56,6 +56,26 @@ def test_noninstantized_bitgen(self):
         assert_raises(ValueError, Generator, MT19937)
 
 
+    def test_seed_init(self):
+        # gh-14844. seed[0] was not correctly initialized
+        # key[0] always held the same value
+
+        class FullSeedSequence(SeedSequence):
+
+            def __init__(self, x):
+                self.x = x
+
+            def generate_state(self, n_words, dtype=np.uint32):
+                return np.full(n_words, self.x, dtype=dtype)
+
+        for i in range(32):
+            ss = FullSeedSequence(1 << i)
+            key = MT19937(ss).state['state']['key']
+            expected = np.full(624, 1 << i, dtype=np.uint32)
+            expected[0] |= 0x80000000
+            np.testing.assert_array_equal(key, expected)
+
+
 class TestBinomial(object):
     def test_n_zero(self):
         # Tests the corner case of n == 0 for the binomial distribution.
@@ -944,7 +964,7 @@ def test_permutation(self):
         arr_2d = np.atleast_2d([1, 2, 3, 4, 5, 6, 7, 8, 9, 0]).T
         actual = random.permutation(arr_2d)
         assert_array_equal(actual, np.atleast_2d(desired).T)
-        
+
         bad_x_str = "abcd"
         assert_raises(np.AxisError, random.permutation, bad_x_str)
 

diff --git a/numpy/random/tests/test_randomstate.py b/numpy/random/tests/test_randomstate.py
@@ -107,6 +107,25 @@ def test_cannot_seed(self):
     def test_invalid_initialization(self):
         assert_raises(ValueError, random.RandomState, MT19937)
 
+    def test_reseed_unique(self):
+        # gh-14844. seed[0] was not correctly re-initialized in legacy seed()
+        # key[0] always held the same value
+        rs = random.RandomState()
+        key = rs._bit_generator.state['state']['key']
+        res = np.empty((32,) + key.shape, dtype=key.dtype)
+        for i in range(32):
+            # enter the _legacy_seed(None) path
+            rs.seed()
+            key = rs._bit_generator.state['state']['key']
+            res[i, ...] = key
+        res.shape = (32, -1)
+        assert not (res[:, 0] == 0x80000000).all()
+
+        rs.seed(np.ones(100, dtype='int64'))
+        k1 = rs._bit_generator.state['state']['key']
+        assert k1[0] != 0x80000000
+
+
 
 class TestBinomial(object):
     def test_n_zero(self):
@@ -618,7 +637,7 @@ def test_choice_nan_probabilities(self):
         a = np.array([42, 1, 2])
         p = [None, None, None]
         assert_raises(ValueError, random.choice, a, p=p)
-    
+
     def test_choice_p_non_contiguous(self):
         p = np.ones(10) / 5
         p[1::2] = 3.0
-Original file line number
+Diff line change
@@ Expand Up @@
         }
       }
-      mt[0] = 0x80000000UL; /* MSB is 1; assuring non-zero initial array */
+      mt[0] |= 0x80000000UL; /* MSB is 1; assuring non-zero initial array */
     }
     void mt19937_gen(mt19937_state *state) {
@@ Expand Down @@