Add a sparse FIR filter implementation

A Finite Impulse Response filter implementation which takes advantage of sparse coefficients.
The coefficients are assumed to be uniformly distributed and have an initial offset.

BUG=webrtc:3146
R=andrew@webrtc.org, bjornv@webrtc.org, kwiberg@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/49659004

Cr-Commit-Position: refs/heads/master@{#9002}

1 files changed, 48 insertions, 0 deletions

diff --git a/webrtc/common_audio/sparse_fir_filter.h b/webrtc/common_audio/sparse_fir_filter.h
new file mode 100644
index 0000000000..f5f3fadcce
--- /dev/null
+++ b/webrtc/common_audio/sparse_fir_filter.h
@@ -0,0 +1,48 @@
+/*
+ *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_COMMON_AUDIO_SPARSE_FIR_FILTER_H_
+#define WEBRTC_COMMON_AUDIO_SPARSE_FIR_FILTER_H_
+
+#include <cstring>
+#include <vector>
+
+namespace webrtc {
+
+// A Finite Impulse Response filter implementation which takes advantage of a
+// sparse structure with uniformly distributed non-zero coefficients.
+class SparseFIRFilter {
+ public:
+  // |num_nonzero_coeffs| is the number of non-zero coefficients,
+  // |nonzero_coeffs|. They are assumed to be uniformly distributed every
+  // |sparsity| samples and with an initial |offset|. The rest of the filter
+  // coefficients will be assumed zeros. For example, with sparsity = 3, and
+  // offset = 1 the filter coefficients will be:
+  // B = [0 coeffs[0] 0 0 coeffs[1] 0 0 coeffs[2] ... ]
+  // All initial state values will be zeros.
+  SparseFIRFilter(const float* nonzero_coeffs,
+                  size_t num_nonzero_coeffs,
+                  size_t sparsity,
+                  size_t offset);
+
+  // Filters the |in| data supplied.
+  // |out| must be previously allocated and it must be at least of |length|.
+  void Filter(const float* in, size_t length, float* out);
+
+ private:
+  const size_t sparsity_;
+  const size_t offset_;
+  const std::vector<float> nonzero_coeffs_;
+  std::vector<float> state_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_COMMON_AUDIO_SPARSE_FIR_FILTER_H_