1 files changed, 65 insertions, 0 deletions
diff --git a/third_party/webrtc/src/webrtc/common_audio/signal_processing/auto_correlation.c b/third_party/webrtc/src/webrtc/common_audio/signal_processing/auto_correlation.c
new file mode 100644
index 00000000..fda4fffe
--- /dev/null
+++ b/third_party/webrtc/src/webrtc/common_audio/signal_processing/auto_correlation.c
@@ -0,0 +1,65 @@
+/*
+ *  Copyright (c) 2012 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.
+ */
+
+#include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
+
+#include <assert.h>
+
+size_t WebRtcSpl_AutoCorrelation(const int16_t* in_vector,
+                                 size_t in_vector_length,
+                                 size_t order,
+                                 int32_t* result,
+                                 int* scale) {
+  int32_t sum = 0;
+  size_t i = 0, j = 0;
+  int16_t smax = 0;
+  int scaling = 0;
+
+  assert(order <= in_vector_length);
+
+  // Find the maximum absolute value of the samples.
+  smax = WebRtcSpl_MaxAbsValueW16(in_vector, in_vector_length);
+
+  // In order to avoid overflow when computing the sum we should scale the
+  // samples so that (in_vector_length * smax * smax) will not overflow.
+  if (smax == 0) {
+    scaling = 0;
+  } else {
+    // Number of bits in the sum loop.
+    int nbits = WebRtcSpl_GetSizeInBits((uint32_t)in_vector_length);
+    // Number of bits to normalize smax.
+    int t = WebRtcSpl_NormW32(WEBRTC_SPL_MUL(smax, smax));
+
+    if (t > nbits) {
+      scaling = 0;
+    } else {
+      scaling = nbits - t;
+    }
+  }
+
+  // Perform the actual correlation calculation.
+  for (i = 0; i < order + 1; i++) {
+    sum = 0;
+    /* Unroll the loop to improve performance. */
+    for (j = 0; i + j + 3 < in_vector_length; j += 4) {
+      sum += (in_vector[j + 0] * in_vector[i + j + 0]) >> scaling;
+      sum += (in_vector[j + 1] * in_vector[i + j + 1]) >> scaling;
+      sum += (in_vector[j + 2] * in_vector[i + j + 2]) >> scaling;
+      sum += (in_vector[j + 3] * in_vector[i + j + 3]) >> scaling;
+    }
+    for (; j < in_vector_length - i; j++) {
+      sum += (in_vector[j] * in_vector[i + j]) >> scaling;
+    }
+    *result++ = sum;
+  }
+
+  *scale = scaling;
+  return order + 1;
+}