Allow same src and dst in InputAudioFile::DuplicateInterleaved

This change allows the input and output to the static method
InputAudioFile::DuplicateInterleaved to be the same array. That is,
in-place manipulation is now possible. A unit test is also added.

R=tina.legrand@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/20239004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7008 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/audio_coding/neteq/tools/input_audio_file.cc

@@ -40,8 +40,11 @@ bool InputAudioFile::Read(size_t samples, int16_t* destination) {
 void InputAudioFile::DuplicateInterleaved(const int16_t* source, size_t samples,
                                           size_t channels,
                                           int16_t* destination) {
-  for (size_t i = 0; i < samples; ++i) {
-    for (size_t j = 0; j < channels; ++j) {
+  // Start from the end of |source| and |destination|, and work towards the
+  // beginning. This is to allow in-place interleaving of the same array (i.e.,
+  // |source| and |destination| are the same array).
+  for (int i = static_cast<int>(samples - 1); i >= 0; --i) {
+    for (int j = static_cast<int>(channels - 1); j >= 0; --j) {
       destination[i * channels + j] = source[i];
     }
   }

webrtc/modules/audio_coding/neteq/tools/input_audio_file.h

@@ -37,7 +37,8 @@ class InputAudioFile {
   // Creates a multi-channel signal from a mono signal. Each sample is repeated
   // |channels| times to create an interleaved multi-channel signal where all
   // channels are identical. The output |destination| must have the capacity to
-  // hold samples * channels elements.
+  // hold samples * channels elements. Note that |source| and |destination| can
+  // be the same array (i.e., point to the same address).
   static void DuplicateInterleaved(const int16_t* source, size_t samples,
                                    size_t channels, int16_t* destination);
 

webrtc/modules/audio_coding/neteq/tools/input_audio_file_unittest.cc

@@ -0,0 +1,58 @@
+/*
+ *  Copyright (c) 2014 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.
+ */
+
+// Unit tests for test InputAudioFile class.
+
+#include "webrtc/modules/audio_coding/neteq/tools/input_audio_file.h"
+
+#include "gtest/gtest.h"
+
+namespace webrtc {
+namespace test {
+
+TEST(TestInputAudioFile, DuplicateInterleaveSeparateSrcDst) {
+  static const size_t kSamples = 10;
+  static const size_t kChannels = 2;
+  int16_t input[kSamples];
+  for (size_t i = 0; i < kSamples; ++i) {
+    input[i] = i;
+  }
+  int16_t output[kSamples * kChannels];
+  InputAudioFile::DuplicateInterleaved(input, kSamples, kChannels, output);
+
+  // Verify output
+  int16_t* output_ptr = output;
+  for (size_t i = 0; i < kSamples; ++i) {
+    for (size_t j = 0; j < kChannels; ++j) {
+      EXPECT_EQ(static_cast<int16_t>(i), *output_ptr++);
+    }
+  }
+}
+
+TEST(TestInputAudioFile, DuplicateInterleaveSameSrcDst) {
+  static const size_t kSamples = 10;
+  static const size_t kChannels = 5;
+  int16_t input[kSamples * kChannels];
+  for (size_t i = 0; i < kSamples; ++i) {
+    input[i] = i;
+  }
+  InputAudioFile::DuplicateInterleaved(input, kSamples, kChannels, input);
+
+  // Verify output
+  int16_t* output_ptr = input;
+  for (size_t i = 0; i < kSamples; ++i) {
+    for (size_t j = 0; j < kChannels; ++j) {
+      EXPECT_EQ(static_cast<int16_t>(i), *output_ptr++);
+    }
+  }
+}
+
+}  // namespace test
+}  // namespace webrtc

webrtc/modules/modules.gyp

@@ -153,6 +153,7 @@
             'audio_coding/neteq/mock/mock_external_decoder_pcm16b.h',
             'audio_coding/neteq/mock/mock_packet_buffer.h',
             'audio_coding/neteq/mock/mock_payload_splitter.h',
+            'audio_coding/neteq/tools/input_audio_file_unittest.cc',
             'audio_coding/neteq/tools/packet_unittest.cc',
             'audio_processing/aec/system_delay_unittest.cc',
             'audio_processing/aec/echo_cancellation_unittest.cc',