added LPCNet torch implementation

Signed-off-by: Jan Buethe <jbuethe@amazon.de>

dnn/torch/lpcnet/utils/misc.py

@@ -0,0 +1,36 @@
+import torch
+
+
+def find(a, v):
+    try:
+        idx = a.index(v)
+    except:
+        idx = -1
+    return idx
+
+def interleave_tensors(tensors, dim=-2):
+    """ interleave list of tensors along sequence dimension """
+
+    x = torch.cat([x.unsqueeze(dim) for x in tensors], dim=dim)
+    x = torch.flatten(x, dim - 1, dim)
+
+    return x
+
+def _interleave(x, pcm_levels=256):
+
+    repeats = pcm_levels // (2*x.size(-1))
+    x = x.unsqueeze(-1)
+    p = torch.flatten(torch.repeat_interleave(torch.cat((x, 1 - x), dim=-1), repeats, dim=-1), -2)
+
+    return p
+
+def get_pdf_from_tree(x):
+    pcm_levels = x.size(-1)
+
+    p = _interleave(x[..., 1:2])
+    n = 4
+    while n <= pcm_levels:
+        p = p * _interleave(x[..., n//2:n])
+        n *= 2
+
+    return p