def polyphase_core(x, m, f):
# x = input data
# m = decimation rate
# f = filter
# Hack job - append zeros to match decimation rate
if x.shape[0] % m != 0:
x = np.append(x, np.zeros((m - x.shape[0] % m,)))
if f.shape[0] % m != 0:
f = np.append(f, np.zeros((m - f.shape[0] % m,)))
polyphase = p = np.zeros((m, (x.shape[0] + f.shape[0]) / m), dtype=x.dtype)
p[0, :-1] = np.convolve(x[::m], f[::m])
# Invert the x values when applying filters
for i in range(1, m):
p[i, 1:] = np.convolve(x[m - i::m], f[i::m])
return p
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