Add a real FFT wrapper around the complex FFT.

BUG=issue762

Review URL: https://webrtc-codereview.appspot.com/769004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2703 4adac7df-926f-26a2-2b94-8c16560cd09d

src/common_audio/signal_processing/include/real_fft.h

@@ -0,0 +1,37 @@
+/*
+ *  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 "typedefs.h"
+
+struct RealFFT;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// TODO(andrew): documentation.
+struct RealFFT* WebRtcSpl_CreateRealFFT(int order);
+void WebRtcSpl_FreeRealFFT(struct RealFFT* self);
+
+// TODO(andrew): This currently functions exactly the same as ComplexFFT().
+// Manage the surrounding operations (ComplexBitReverse etc) here instead.
+//
+// data must be of length 2^(order + 1) to hold the complex output.
+int WebRtcSpl_RealForwardFFT(struct RealFFT* self, int16_t* data);
+int WebRtcSpl_RealInverseFFT(struct RealFFT* self, int16_t* data);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // WEBRTC_COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_

src/common_audio/signal_processing/real_fft.c

@@ -0,0 +1,42 @@
+/*
+ *  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 "common_audio/signal_processing/include/real_fft.h"
+
+#include <stdlib.h>
+
+#include "common_audio/signal_processing/include/signal_processing_library.h"
+
+struct RealFFT {
+  int order;
+};
+
+struct RealFFT* WebRtcSpl_CreateRealFFT(int order) {
+  struct RealFFT* self = NULL;
+  // This constraint comes from ComplexFFT().
+  if (order > 10 || order < 0) {
+    return NULL;
+  }
+  self = malloc(sizeof(struct RealFFT));
+  self->order = order;
+  return self;
+}
+
+void WebRtcSpl_FreeRealFFT(struct RealFFT* self) {
+  free(self);
+}
+
+int WebRtcSpl_RealForwardFFT(struct RealFFT* self, int16_t* data) {
+  return WebRtcSpl_ComplexFFT(data, self->order, 1);
+}
+
+int WebRtcSpl_RealInverseFFT(struct RealFFT* self, int16_t* data) {
+  return WebRtcSpl_ComplexIFFT(data, self->order, 1);
+}

src/common_audio/signal_processing/real_fft_unittest.cc

@@ -0,0 +1,85 @@
+/*
+ *  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 "common_audio/signal_processing/include/real_fft.h"
+#include "common_audio/signal_processing/include/signal_processing_library.h"
+#include "typedefs.h"
+
+#include "gtest/gtest.h"
+
+namespace webrtc {
+namespace {
+
+const int kOrder = 3;
+const int kLength = 1 << (kOrder + 1);  // +1 to hold complex data.
+const int16_t kRefData[kLength] = {
+    11739, -6848, -8688, 31980, -30295, 25242, 27085, 19410, -26299, -15607,
+    -10791, 11778, -23819, 14498, -25772, 10076
+};
+
+class RealFFTTest : public ::testing::Test {
+};
+
+TEST_F(RealFFTTest, CreateFailsOnBadInput) {
+  RealFFT* fft = WebRtcSpl_CreateRealFFT(11);
+  EXPECT_TRUE(fft == NULL);
+  fft = WebRtcSpl_CreateRealFFT(-1);
+  EXPECT_TRUE(fft == NULL);
+}
+
+// TODO(andrew): Look more into why this was failing.
+TEST_F(RealFFTTest, DISABLED_TransformIsInvertible) {
+  int16_t data[kLength] = {0};
+  memcpy(data, kRefData, sizeof(kRefData));
+
+  RealFFT* fft = NULL;
+  fft = WebRtcSpl_CreateRealFFT(kOrder);
+  EXPECT_TRUE(fft != NULL);
+
+  EXPECT_EQ(0, WebRtcSpl_RealForwardFFT(fft, data));
+  int scale = WebRtcSpl_RealInverseFFT(fft, data);
+
+  EXPECT_GE(scale, 0);
+  for (int i = 0; i < kLength; i++) {
+    EXPECT_EQ(data[i] << scale, kRefData[i]);
+  }
+  WebRtcSpl_FreeRealFFT(fft);
+}
+
+// TODO(andrew): This won't always be the case, but verifies the current code
+// at least.
+TEST_F(RealFFTTest, RealAndComplexAreIdentical) {
+  int16_t real_data[kLength] = {0};
+  int16_t complex_data[kLength] = {0};
+  memcpy(real_data, kRefData, sizeof(kRefData));
+  memcpy(complex_data, kRefData, sizeof(kRefData));
+
+  RealFFT* fft = NULL;
+  fft = WebRtcSpl_CreateRealFFT(kOrder);
+  EXPECT_TRUE(fft != NULL);
+
+  EXPECT_EQ(0, WebRtcSpl_RealForwardFFT(fft, real_data));
+  EXPECT_EQ(0, WebRtcSpl_ComplexFFT(complex_data, kOrder, 1));
+  for (int i = 0; i < kLength; i++) {
+    EXPECT_EQ(real_data[i], complex_data[i]);
+  }
+
+  int real_scale =  WebRtcSpl_RealInverseFFT(fft, real_data);
+  int complex_scale = WebRtcSpl_ComplexIFFT(complex_data, kOrder, 1);
+  EXPECT_GE(real_scale, 0);
+  EXPECT_EQ(real_scale, complex_scale);
+  for (int i = 0; i < kLength; i++) {
+    EXPECT_EQ(real_data[i], complex_data[i]);
+  }
+  WebRtcSpl_FreeRealFFT(fft);
+}
+
+}  // namespace
+}  // namespace webrtc

src/common_audio/signal_processing/signal_processing.gypi

@@ -20,6 +20,7 @@
         ],
       },
       'sources': [
+        'include/real_fft.h',
         'include/signal_processing_library.h',
         'include/spl_inl.h',
         'auto_corr_to_refl_coef.c',
@@ -43,6 +44,7 @@
         'min_max_operations.c',
         'randomization_functions.c',
         'refl_coef_to_lpc.c',
+        'real_fft.c',
         'resample.c',
         'resample_48khz.c',
         'resample_by_2.c',
@@ -100,10 +102,11 @@
           'type': 'executable',
           'dependencies': [
             'signal_processing',
-            '<(webrtc_root)/test/test.gyp:test_support_main',
             '<(DEPTH)/testing/gtest.gyp:gtest',
+            '<(webrtc_root)/test/test.gyp:test_support_main',
           ],
           'sources': [
+            'real_fft_unittest.cc',
             'signal_processing_unittest.cc',
           ],
         }, # spl_unittests