refactor sampling

sampling.py

@@ -0,0 +1,58 @@
+import numpy as np
+
+class Interpolator(object):
+    def __init__(self, resolution=10000, width=128):
+        self.width = width
+        self.resolution = resolution
+        self.N = resolution * width
+        u = np.arange(-self.N, self.N, dtype=float)
+        window = (1 + np.cos(0.5 * np.pi * u / self.N)) / 2.0
+        h = np.sinc(u / resolution) * window
+        self.filt = []
+        for index in range(resolution):  # split into multiphase filters
+            filt = h[index::resolution]
+            filt = filt[::-1]
+            self.filt.append(filt)
+        lengths = map(len, self.filt)
+        assert set(lengths) == set([2*width])
+        assert len(self.filt) == resolution
+
+    def get(self, offset):
+        # offset = k + (j / self.resolution)
+        k = int(offset)
+        j = int((offset - k) * self.resolution)
+        coeffs = self.filt[j]
+        return coeffs, k - self.width
+
+class Sampler(object):
+    def __init__(self, src, interp):
+        self.src = iter(src)
+        self.freq = 1.0
+        self.interp = interp
+        coeffs, begin = self.interp.get(0)
+        self.offset = -begin  # should fill samples buffer
+        self.buff = np.zeros(len(coeffs))
+        self.index = 0
+
+    def __iter__(self):
+        return self
+
+    def correct(self, offset=0):
+        assert self.freq + offset > 0
+        self.offset += offset
+
+    def next(self):
+        res = self._sample()
+        self.offset += self.freq
+        return res
+
+    def _sample(self):
+        coeffs, begin = self.interp.get(self.offset)
+        end = begin + len(coeffs)
+        while True:
+            if self.index == end:
+                return np.dot(coeffs, self.buff)
+
+            self.buff[:-1] = self.buff[1:]
+            self.buff[-1] = self.src.next()  # throws StopIteration
+            self.index += 1