Mix to an intermediate buffer.

services/media/audio/platform/generic/mixers/mixer_utils.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SERVICES_MEDIA_AUDIO_PLATFORM_GENERIC_MIXERS_MIXER_UTILS_H_
 #define SERVICES_MEDIA_AUDIO_PLATFORM_GENERIC_MIXERS_MIXER_UTILS_H_
 
 #include <limits>
 #include <type_traits>
 
 namespace mojo {
 namespace media {
 namespace audio {
 namespace mixers {
 namespace utils {
 
 // mixer_utils.h is a collection of inline templated utility functions meant to
 // be used by mixer implementations and expanded/optimized at compile time in
 // order to produce efficient inner mixing loops for all of the different
 // variations of source/destination sample type/channel counts.
 
-// Template to read samples and normalize them into signed 32 bit integers.
+// Template to read samples and normalize them into signed 16 bit integers
+// stored in 32 bit integers.
 template <typename SType, typename Enable = void> class SampleNormalizer;
 
 template <typename SType>
 class SampleNormalizer<
       SType,
       typename std::enable_if<
         std::is_same<SType, uint8_t>::value,
       void>::type> {
  public:
   static inline int32_t Read(const SType* src) {
@@ skipping 44 matching lines @@
         (SChCount == 2) && (DChCount == 1),
       void>::type> {
  public:
   static constexpr size_t DstPerSrc = 1;
   static inline int32_t Read(const SType* src) {
     return (SampleNormalizer<SType>::Read(src + 0) +
             SampleNormalizer<SType>::Read(src + 1)) >> 1;
   }
 };
 
-// Template to produce destination samples from normalized samples.
-template <typename DType, typename Enable = void> class DstConverter;
-
-template <typename DType>
-class DstConverter<DType,
-      typename std::enable_if<
-        std::is_same<DType, int16_t>::value,
-      void>::type> {
- public:
-  static inline DType Convert(int32_t sample) {
-    return static_cast<DType>(sample);
-  }
-};
-
-template <typename DType>
-class DstConverter<DType,
-      typename std::enable_if<
-        std::is_same<DType, uint8_t>::value,
-      void>::type> {
- public:
-  static inline DType Convert(int32_t sample) {
-    return static_cast<DType>((sample >> 8) + 0x80);
-  }
-};
-
-// Template to mix destination samples with normalized source samples based on
-// accumulation policy.
-template <typename DType,
-          bool     DoAccumulate,
+// Template to mix normalized destination samples with normalized source samples
+// based on accumulation policy.
+template <bool     DoAccumulate,
           typename Enable = void>
 class DstMixer;
 
-template <typename DType,
-          bool     DoAccumulate>
-class DstMixer<DType, DoAccumulate,
+template <bool DoAccumulate>
+class DstMixer<DoAccumulate,
       typename std::enable_if<
         DoAccumulate == false,
       void>::type> {
  public:
-  static inline int32_t Mix(const DType* dst, uint32_t sample) {
-    return DstConverter<DType>::Convert(sample);
+  static inline constexpr int32_t Mix(int32_t dst, int32_t sample) {
+    return sample;
   }
 };
 
-template <typename DType,
-          bool     DoAccumulate>
-class DstMixer<DType, DoAccumulate,
+template <bool DoAccumulate>
+class DstMixer<DoAccumulate,
       typename std::enable_if<
         DoAccumulate == true,
       void>::type> {
  public:
-  static inline int32_t Mix(const DType* dst, int32_t sample) {
-    sample += SampleNormalizer<DType>::Read(dst);
-
-    if (sample > std::numeric_limits<int16_t>::max()) {
-      return DstConverter<DType>::Convert(std::numeric_limits<int16_t>::max());
-    } else if (sample < std::numeric_limits<int16_t>::min()) {
-      return DstConverter<DType>::Convert(std::numeric_limits<int16_t>::min());
-    } else {
-      return DstConverter<DType>::Convert(sample);
-    }
+  static inline constexpr int32_t Mix(int32_t dst, int32_t sample) {
+    return sample + dst;
   }
 };
 
 
 }  // namespace utils
 }  // namespace mixers
 }  // namespace audio
 }  // namespace media
 }  // namespace mojo
 
 #endif  // SERVICES_MEDIA_AUDIO_PLATFORM_GENERIC_MIXERS_MIXER_UTILS_H_