Fix out-of-range integer brng reading past brng_list

CHANGELOG.md

@@ -20,6 +20,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Extended the `memcpy`-based fast path of `shuffle` to multi-dimensional `ndarray` inputs whose first-axis items are contiguous, which is also much faster than the previous buffered path [gh-159](https://github.com/IntelPython/mkl_random/pull/159)
 
 ### Fixed
+* Fixed an out-of-range integer `brng` indexing `brng_list` past its end, which returned uninitialized memory as random values; it now warns and falls back to `MT19937`
+* Fixed `brng=0` being treated as unset, which left the state unseeded
 * Fixed `uniform` to return a Python `float` for scalar bounds with `size=None` instead of a 0-d array [gh-167](https://github.com/IntelPython/mkl_random/pull/167)
 * Fixed `randint` returning `high` for `int64`, `uint64` and the default `int` dtype when the range is at or above `INT_MAX` [gh-172](https://github.com/IntelPython/mkl_random/pull/172)
 * Fixed the integer fills silently under-filling requests larger than two `MKL_INT_MAX` chunks [gh-172](https://github.com/IntelPython/mkl_random/pull/172)

mkl_random/mklrand.pyx

@@ -64,6 +64,8 @@ cdef extern from "numpy_multiiter_workaround.h":
 
 cdef extern from "randomkit.h":
 
+    int BRNG_KINDS
+
     ctypedef struct irk_state:
         pass
 
@@ -1575,7 +1577,12 @@ cdef irk_brng_t _parse_brng_token_(brng):
         else:
             brng_token = tmp
     elif isinstance(brng, int):
-        brng_token = operator.index(brng)
+        # Out of range would index brng_list past its end in the seeding routines.
+        tmp = operator.index(brng)
+        if 0 <= tmp < BRNG_KINDS:
+            brng_token = tmp
+        else:
+            brng_token = _default_fallback_brng_token_(brng)
     else:
         brng_token = _default_fallback_brng_token_(brng)
 
@@ -1643,8 +1650,10 @@ cdef class _MKLRandomState:
         cdef unsigned int stream_id
         cdef cnp.ndarray obj "arrayObject_obj"
         cdef bint use_array = False
+        # Not truthiness: 0 is falsy but is MT19937.
+        cdef bint brng_given = brng is not None
 
-        if (brng):
+        if brng_given:
             # Parse before the lock to avoid warn
             brng_token, stream_id = _parse_brng_argument(brng)
 
@@ -1670,7 +1679,7 @@ cdef class _MKLRandomState:
                 obj = obj.astype("uint32", casting="unsafe", order="C")
 
         with self.lock:
-            if not brng:
+            if not brng_given:
                 # Reads state->stream, which a concurrent seed can free.
                 brng_token = <irk_brng_t> irk_get_brng_and_stream_mkl(
                     self.internal_state, &stream_id

mkl_random/tests/test_random.py

@@ -107,6 +107,24 @@ def test_non_deterministic_brng():
     assert isinstance(v, int)
 
 
+@pytest.mark.parametrize("brng", [11, 15, 99, -1, -100])
+def test_out_of_range_integer_brng_falls_back(brng):
+    with pytest.warns(UserWarning, match="not recognized"):
+        rs = rnd.MKLRandomState(1, brng=brng)
+
+    expected = rnd.MKLRandomState(1, brng="MT19937").randint(0, 100, 8)
+    assert_equal(rs.randint(0, 100, 8), expected)
+
+
+@pytest.mark.parametrize("brng_id,name", [(0, "MT19937"), (10, "ARS5")])
+def test_boundary_integer_brng_accepted(brng_id, name):
+    with assert_no_warnings():
+        rs = rnd.MKLRandomState(1, brng=brng_id)
+
+    expected = rnd.MKLRandomState(1, brng=name).randint(0, 100, 8)
+    assert_equal(rs.randint(0, 100, 8), expected)
+
+
 def test_binomial_n_zero():
     zeros = np.zeros(2, dtype="int32")
     for p in [0, 0.5, 1]: