Update common_audio

Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1

Update notes:

 * Moved src/ to webrtc/ to easily diff against the third_party/webrtc
   in the chromium tree

 * ARM/NEON/MIPS support is not yet hooked up

 * Tests have not been copied

webrtc/common_audio/signal_processing/include/real_fft.h

@@ -0,0 +1,97 @@
+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_
+#define WEBRTC_COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_
+
+#include "webrtc/typedefs.h"
+
+// For ComplexFFT(), the maximum fft order is 10;
+// for OpenMax FFT in ARM, it is 12;
+// WebRTC APM uses orders of only 7 and 8.
+enum {kMaxFFTOrder = 10};
+
+struct RealFFT;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct RealFFT* WebRtcSpl_CreateRealFFT(int order);
+void WebRtcSpl_FreeRealFFT(struct RealFFT* self);
+
+// Compute an FFT for a real-valued signal of length of 2^order,
+// where 1 < order <= MAX_FFT_ORDER. Transform length is determined by the
+// specification structure, which must be initialized prior to calling the FFT
+// function with WebRtcSpl_CreateRealFFT().
+// The relationship between the input and output sequences can
+// be expressed in terms of the DFT, i.e.:
+//     x[n] = (2^(-scalefactor)/N)  . SUM[k=0,...,N-1] X[k].e^(jnk.2.pi/N)
+//     n=0,1,2,...N-1
+//     N=2^order.
+// The conjugate-symmetric output sequence is represented using a CCS vector,
+// which is of length N+2, and is organized as follows:
+//     Index:      0  1  2  3  4  5   . . .   N-2       N-1       N       N+1
+//     Component:  R0 0  R1 I1 R2 I2  . . .   R[N/2-1]  I[N/2-1]  R[N/2]  0
+// where R[n] and I[n], respectively, denote the real and imaginary components
+// for FFT bin 'n'. Bins  are numbered from 0 to N/2, where N is the FFT length.
+// Bin index 0 corresponds to the DC component, and bin index N/2 corresponds to
+// the foldover frequency.
+//
+// Input Arguments:
+//   self - pointer to preallocated and initialized FFT specification structure.
+//   real_data_in - the input signal. For an ARM Neon platform, it must be
+//                  aligned on a 32-byte boundary.
+//
+// Output Arguments:
+//   complex_data_out - the output complex signal with (2^order + 2) 16-bit
+//                      elements. For an ARM Neon platform, it must be different
+//                      from real_data_in, and aligned on a 32-byte boundary.
+//
+// Return Value:
+//   0  - FFT calculation is successful.
+//   -1 - Error with bad arguments (NULL pointers).
+int WebRtcSpl_RealForwardFFT(struct RealFFT* self,
+                             const int16_t* real_data_in,
+                             int16_t* complex_data_out);
+
+// Compute the inverse FFT for a conjugate-symmetric input sequence of length of
+// 2^order, where 1 < order <= MAX_FFT_ORDER. Transform length is determined by
+// the specification structure, which must be initialized prior to calling the
+// FFT function with WebRtcSpl_CreateRealFFT().
+// For a transform of length M, the input sequence is represented using a packed
+// CCS vector of length M+2, which is explained in the comments for
+// WebRtcSpl_RealForwardFFTC above.
+//
+// Input Arguments:
+//   self - pointer to preallocated and initialized FFT specification structure.
+//   complex_data_in - the input complex signal with (2^order + 2) 16-bit
+//                     elements. For an ARM Neon platform, it must be aligned on
+//                     a 32-byte boundary.
+//
+// Output Arguments:
+//   real_data_out - the output real signal. For an ARM Neon platform, it must
+//                   be different to complex_data_in, and aligned on a 32-byte
+//                   boundary.
+//
+// Return Value:
+//   0 or a positive number - a value that the elements in the |real_data_out|
+//                            should be shifted left with in order to get
+//                            correct physical values.
+//   -1 - Error with bad arguments (NULL pointers).
+int WebRtcSpl_RealInverseFFT(struct RealFFT* self,
+                             const int16_t* complex_data_in,
+                             int16_t* real_data_out);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // WEBRTC_COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_