1 files changed, 102 insertions, 0 deletions
diff --git a/third_party/webrtc/src/webrtc/common_audio/signal_processing/real_fft.c b/third_party/webrtc/src/webrtc/common_audio/signal_processing/real_fft.c
new file mode 100644
index 00000000..92daae4d
--- /dev/null
+++ b/third_party/webrtc/src/webrtc/common_audio/signal_processing/real_fft.c
@@ -0,0 +1,102 @@
+/*
+ *  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/real_fft.h"
+
+#include <stdlib.h>
+
+#include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
+
+struct RealFFT {
+  int order;
+};
+
+struct RealFFT* WebRtcSpl_CreateRealFFT(int order) {
+  struct RealFFT* self = NULL;
+
+  if (order > kMaxFFTOrder || order < 0) {
+    return NULL;
+  }
+
+  self = malloc(sizeof(struct RealFFT));
+  if (self == NULL) {
+    return NULL;
+  }
+  self->order = order;
+
+  return self;
+}
+
+void WebRtcSpl_FreeRealFFT(struct RealFFT* self) {
+  if (self != NULL) {
+    free(self);
+  }
+}
+
+// The C version FFT functions (i.e. WebRtcSpl_RealForwardFFT and
+// WebRtcSpl_RealInverseFFT) are real-valued FFT wrappers for complex-valued
+// FFT implementation in SPL.
+
+int WebRtcSpl_RealForwardFFT(struct RealFFT* self,
+                             const int16_t* real_data_in,
+                             int16_t* complex_data_out) {
+  int i = 0;
+  int j = 0;
+  int result = 0;
+  int n = 1 << self->order;
+  // The complex-value FFT implementation needs a buffer to hold 2^order
+  // 16-bit COMPLEX numbers, for both time and frequency data.
+  int16_t complex_buffer[2 << kMaxFFTOrder];
+
+  // Insert zeros to the imaginary parts for complex forward FFT input.
+  for (i = 0, j = 0; i < n; i += 1, j += 2) {
+    complex_buffer[j] = real_data_in[i];
+    complex_buffer[j + 1] = 0;
+  };
+
+  WebRtcSpl_ComplexBitReverse(complex_buffer, self->order);
+  result = WebRtcSpl_ComplexFFT(complex_buffer, self->order, 1);
+
+  // For real FFT output, use only the first N + 2 elements from
+  // complex forward FFT.
+  memcpy(complex_data_out, complex_buffer, sizeof(int16_t) * (n + 2));
+
+  return result;
+}
+
+int WebRtcSpl_RealInverseFFT(struct RealFFT* self,
+                             const int16_t* complex_data_in,
+                             int16_t* real_data_out) {
+  int i = 0;
+  int j = 0;
+  int result = 0;
+  int n = 1 << self->order;
+  // Create the buffer specific to complex-valued FFT implementation.
+  int16_t complex_buffer[2 << kMaxFFTOrder];
+
+  // For n-point FFT, first copy the first n + 2 elements into complex
+  // FFT, then construct the remaining n - 2 elements by real FFT's
+  // conjugate-symmetric properties.
+  memcpy(complex_buffer, complex_data_in, sizeof(int16_t) * (n + 2));
+  for (i = n + 2; i < 2 * n; i += 2) {
+    complex_buffer[i] = complex_data_in[2 * n - i];
+    complex_buffer[i + 1] = -complex_data_in[2 * n - i + 1];
+  }
+
+  WebRtcSpl_ComplexBitReverse(complex_buffer, self->order);
+  result = WebRtcSpl_ComplexIFFT(complex_buffer, self->order, 1);
+
+  // Strip out the imaginary parts of the complex inverse FFT output.
+  for (i = 0, j = 0; i < n; i += 1, j += 2) {
+    real_data_out[i] = complex_buffer[j];
+  }
+
+  return result;
+}