| // Copyright 2016 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 COBALT_MEDIA_BASE_AUDIO_SAMPLE_TYPES_H_ |
| #define COBALT_MEDIA_BASE_AUDIO_SAMPLE_TYPES_H_ |
| |
| #include <cstdint> |
| #include <limits> |
| #include <type_traits> |
| |
| // To specify different sample formats, we provide a class for each sample |
| // format that knows certain things about it, such as the C++ data type used |
| // to store sample values, min and max values, as well as how to convert to |
| // and from floating point formats. Each class must satisfy a concept we call |
| // "SampleTypeTraits", which requires that the following publics are provided: |
| // * A type |ValueType| specifying the C++ type for storing sample values |
| // * A static constant kMinValue which specifies the minimum sample value |
| // * A static constant kMaxValue which specifies the maximum sample value |
| // * A static constant kZeroPointValue which specifies the sample value |
| // representing an amplitude of zero |
| // * A static method ConvertFromFloat() that takes a float sample value and |
| // converts it to the corresponding ValueType |
| // * A static method ConvertFromDouble() that takes a double sample value and |
| // converts it to the corresponding ValueType |
| // * A static method ConvertToFloat() that takes a ValueType sample value and |
| // converts it to the corresponding float value |
| // * A static method ConvertToDouble() that takes a ValueType sample value and |
| // converts it to the corresponding double value |
| |
| namespace cobalt { |
| namespace media { |
| |
| // For float or double. |
| // See also the aliases for commonly used types at the bottom of this file. |
| template <typename SampleType> |
| class FloatSampleTypeTraits { |
| static_assert(std::is_floating_point<SampleType>::value, |
| "Template is only valid for float types."); |
| |
| public: |
| using ValueType = SampleType; |
| |
| static constexpr SampleType kMinValue = -1.0f; |
| static constexpr SampleType kMaxValue = +1.0f; |
| static constexpr SampleType kZeroPointValue = 0.0f; |
| |
| static SampleType FromFloat(float source_value) { |
| return From<float>(source_value); |
| } |
| static float ToFloat(SampleType source_value) { |
| return To<float>(source_value); |
| } |
| static SampleType FromDouble(double source_value) { |
| return From<double>(source_value); |
| } |
| static double ToDouble(SampleType source_value) { |
| return To<double>(source_value); |
| } |
| |
| private: |
| template <typename FloatType> |
| static SampleType From(FloatType source_value) { |
| return static_cast<SampleType>(source_value); |
| } |
| |
| template <typename FloatType> |
| static FloatType To(SampleType source_value) { |
| return static_cast<FloatType>(source_value); |
| } |
| }; |
| |
| // For uint8_t, int16_t, int32_t... |
| // See also the aliases for commonly used types at the bottom of this file. |
| template <typename SampleType> |
| class FixedSampleTypeTraits { |
| static_assert(std::numeric_limits<SampleType>::is_integer, |
| "Template is only valid for integer types."); |
| |
| public: |
| using ValueType = SampleType; |
| |
| static constexpr SampleType kMinValue = |
| std::numeric_limits<SampleType>::min(); |
| static constexpr SampleType kMaxValue = |
| std::numeric_limits<SampleType>::max(); |
| static constexpr SampleType kZeroPointValue = |
| (kMinValue == 0) ? (kMaxValue / 2 + 1) : 0; |
| |
| static SampleType FromFloat(float source_value) { |
| return From<float>(source_value); |
| } |
| static float ToFloat(SampleType source_value) { |
| return To<float>(source_value); |
| } |
| static SampleType FromDouble(double source_value) { |
| return From<double>(source_value); |
| } |
| static double ToDouble(SampleType source_value) { |
| return To<double>(source_value); |
| } |
| |
| private: |
| // We pre-compute the scaling factors for conversion at compile-time in order |
| // to save computation time during runtime. |
| template <typename FloatType> |
| struct ScalingFactors { |
| // Since zero_point_value() is not the exact center between |
| // min_value() and max_value(), we apply a different scaling for positive |
| // and negative values. |
| // Note that due to the limited precision, the FloatType values may not |
| // always be able to represent the max and min values of the integer |
| // SampleType exactly. This is a concern when using these scale factors for |
| // scaling input sample values for conversion. However, since the min value |
| // of SampleType is usually of the form -2^N and the max value is usually of |
| // the form (+2^N)-1, and due to the fact that the float types store a |
| // significand value plus a binary exponent it just so happens that |
| // FloatType can usually represent the min value exactly and its |
| // representation of the max value is only off by 1, i.e. it quantizes to |
| // (+2^N) instead of (+2^N-1). |
| |
| static constexpr FloatType kForPositiveInput = |
| static_cast<FloatType>(kMaxValue) - |
| static_cast<FloatType>(kZeroPointValue); |
| |
| // Note: In the below expression, it is important that we cast kMinValue to |
| // FloatType _before_ taking the negative of it. For example, for SampleType |
| // int32_t, the expression (- kMinValue) would evaluate to |
| // -numeric_limits<int32_t>::min(), which falls outside the numeric |
| // range, wraps around, and ends up being the same as |
| // +numeric_limits<int32_t>::min(). |
| static constexpr FloatType kForNegativeInput = |
| static_cast<FloatType>(kZeroPointValue) - |
| static_cast<FloatType>(kMinValue); |
| |
| static constexpr FloatType kInverseForPositiveInput = |
| 1.0f / kForPositiveInput; |
| |
| static constexpr FloatType kInverseForNegativeInput = |
| 1.0f / kForNegativeInput; |
| }; |
| |
| template <typename FloatType> |
| static SampleType From(FloatType source_value) { |
| // Note, that the for the case of |source_value| == 1.0, the imprecision of |
| // |kScalingFactorForPositive| can lead to a product that is larger than the |
| // maximum possible value of SampleType. To ensure this does not happen, we |
| // handle the case of |source_value| == 1.0 as part of the clipping check. |
| // For all FloatType values smaller than 1.0, the imprecision of |
| // |kScalingFactorForPositive| is small enough to not push the scaled |
| // |source_value| outside the numeric range of SampleType. |
| |
| // The nested if/else structure appears to compile to a |
| // better-performing release binary compared to handling the clipping for |
| // both positive and negative values first. |
| // |
| // Inlining the computation formula for multiplication with the scaling |
| // factor and addition of |kZeroPointValue| results in better performance |
| // for the int16_t case on Arm when compared to storing the scaling factor |
| // in a temporary variable and applying it outside of the if-else block. |
| // |
| // It is important to have the cast to SampleType take place _after_ |
| // adding |kZeroPointValue|, because the scaled source value may be negative |
| // and SampleType may be an unsigned integer type. The result of casting a |
| // negative float to an unsigned integer is undefined. |
| if (source_value < 0) { |
| // Apply clipping (aka. clamping). |
| if (source_value <= FloatSampleTypeTraits<float>::kMinValue) |
| return kMinValue; |
| |
| return static_cast<SampleType>( |
| (source_value * ScalingFactors<FloatType>::kForNegativeInput) + |
| static_cast<FloatType>(kZeroPointValue)); |
| } else { |
| // Apply clipping (aka. clamping). |
| // As mentioned above, here we must include the case |source_value| == 1. |
| if (source_value >= FloatSampleTypeTraits<float>::kMaxValue) |
| return kMaxValue; |
| return static_cast<SampleType>( |
| (source_value * ScalingFactors<FloatType>::kForPositiveInput) + |
| static_cast<FloatType>(kZeroPointValue)); |
| } |
| } |
| |
| template <typename FloatType> |
| static FloatType To(SampleType source_value) { |
| FloatType offset_value = |
| static_cast<FloatType>(source_value - kZeroPointValue); |
| |
| // We multiply with the inverse scaling factor instead of dividing by the |
| // scaling factor, because multiplication performs faster than division |
| // on many platforms. |
| return (offset_value < 0.0f) |
| ? (offset_value * |
| ScalingFactors<FloatType>::kInverseForNegativeInput) |
| : (offset_value * |
| ScalingFactors<FloatType>::kInverseForPositiveInput); |
| } |
| }; |
| |
| // Aliases for commonly used sample formats. |
| using Float32SampleTypeTraits = FloatSampleTypeTraits<float>; |
| using Float64SampleTypeTraits = FloatSampleTypeTraits<double>; |
| using UnsignedInt8SampleTypeTraits = FixedSampleTypeTraits<uint8_t>; |
| using SignedInt16SampleTypeTraits = FixedSampleTypeTraits<int16_t>; |
| using SignedInt32SampleTypeTraits = FixedSampleTypeTraits<int32_t>; |
| |
| } // namespace media |
| } // namespace cobalt |
| |
| #endif // COBALT_MEDIA_BASE_AUDIO_SAMPLE_TYPES_H_ |