Merge pull request #16551 from numpy/fix/seed-sequence-zeros

BUG: Ensure SeedSequence 0-padding does not collide with spawn keys

1 files changed, 10 insertions, 1 deletions

diff --git a/numpy/random/bit_generator.pyx b/numpy/random/bit_generator.pyx
index f145ec13d..3c52a9933 100644
--- a/numpy/random/bit_generator.pyx
+++ b/numpy/random/bit_generator.pyx
@@ -382,13 +382,22 @@ cdef class SeedSequence():
         -------
         entropy_array : 1D uint32 array
         """
-        # Convert run-entropy, program-entropy, and the spawn key into uint32
+        # Convert run-entropy and the spawn key into uint32
         # arrays and concatenate them.
 
         # We MUST have at least some run-entropy. The others are optional.
         assert self.entropy is not None
         run_entropy = _coerce_to_uint32_array(self.entropy)
         spawn_entropy = _coerce_to_uint32_array(self.spawn_key)
+        if len(spawn_entropy) > 0 and len(run_entropy) < self.pool_size:
+            # Explicitly fill out the entropy with 0s to the pool size to avoid
+            # conflict with spawn keys. We changed this in 1.19.0 to fix
+            # gh-16539. In order to preserve stream-compatibility with
+            # unspawned SeedSequences with small entropy inputs, we only do
+            # this when a spawn_key is specified.
+            diff = self.pool_size - len(run_entropy)
+            run_entropy = np.concatenate(
+                [run_entropy, np.zeros(diff, dtype=np.uint32)])
         entropy_array = np.concatenate([run_entropy, spawn_entropy])
         return entropy_array