refactor: add warning for missing _C*.so file and check extension loading in Recurrence

Author: yoyolicoris

torchlpc/__init__.py

@@ -1,6 +1,7 @@
 import torch
 from typing import Optional
 from pathlib import Path
+import warnings
 
 so_files = list(Path(__file__).parent.glob("_C*.so"))
 # assert len(so_files) == 1, f"Expected one _C*.so file, found {len(so_files)}"
@@ -10,6 +11,7 @@
 elif len(so_files) > 1:
     raise ValueError(f"Expected one _C*.so file, found {len(so_files)}")
 else:
+    warnings.warn("No _C*.so file found. Custom extension not loaded.")
     EXTENSION_LOADED = False
 
 from .core import LPC

torchlpc/recurrence.py

@@ -6,6 +6,7 @@
 
 from .parallel_scan import compute_linear_recurrence, WARPSIZE
 from .core import lpc_cuda, lpc_np
+from . import EXTENSION_LOADED
 
 
 class Recurrence(Function):
@@ -32,7 +33,7 @@ def forward(
         else:
             num_threads = torch.get_num_threads()
             # This is just a rough estimation of the computational cost
-            if min(n_dims, num_threads) < num_threads / 3:
+            if EXTENSION_LOADED and min(n_dims, num_threads) < num_threads / 3:
                 out = torch.ops.torchlpc.scan_cpu(impulse, decay, initial_state)
             else:
                 out = torch.from_numpy(