add webrtc-audio-coding public library

This new lib contains the bare minimum to implement an iSAC encoder and
decoder.

The webrtc files have been copied from the revision as the existing
imported files (c8b569e0a7ad0b369e15f0197b3a558699ec8efa).

webrtc/modules/audio_coding/codecs/isac/main/source/fft.h

@@ -0,0 +1,45 @@
+/*
+ *  Copyright (c) 2011 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.
+ */
+
+/*--------------------------------*-C-*---------------------------------*
+ * File:
+ *       fftn.h
+ * ---------------------------------------------------------------------*
+ * Re[]:        real value array
+ * Im[]:        imaginary value array
+ * nTotal:      total number of complex values
+ * nPass:       number of elements involved in this pass of transform
+ * nSpan:       nspan/nPass = number of bytes to increment pointer
+ *              in Re[] and Im[]
+ * isign: exponent: +1 = forward  -1 = reverse
+ * scaling: normalizing constant by which the final result is *divided*
+ * scaling == -1, normalize by total dimension of the transform
+ * scaling <  -1, normalize by the square-root of the total dimension
+ *
+ * ----------------------------------------------------------------------
+ * See the comments in the code for correct usage!
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_CODING_CODECS_ISAC_MAIN_SOURCE_FFT_H_
+#define WEBRTC_MODULES_AUDIO_CODING_CODECS_ISAC_MAIN_SOURCE_FFT_H_
+
+
+#include "structs.h"
+
+
+/* double precision routine */
+
+
+int WebRtcIsac_Fftns (unsigned int ndim, const int dims[], double Re[], double Im[],
+                     int isign, double scaling, FFTstr *fftstate);
+
+
+
+#endif /* WEBRTC_MODULES_AUDIO_CODING_CODECS_ISAC_MAIN_SOURCE_FFT_H_ */