使用getter时UnsafeMutableBufferPointer速度较慢

Question

我有一个带有自定义AURenderCallback的AVAudioEngine。当我运行的引擎，CPU峰值起来，它似乎已经与UnsafeMutableBufferPointer.getter和.setter行动做：

func performRender(ioActionFlags: UnsafeMutablePointer<AudioUnitRenderActionFlags>, inTimeStamp: UnsafePointer<AudioTimeStamp>, inBusNumber: UInt32, inNumberFrames: UInt32, ioData: UnsafeMutablePointer<AudioBufferList>?) -> OSStatus { 

    let blI = UnsafeMutableAudioBufferListPointer(ioData) 

    let numSamples = Int((blI?[0].mDataByteSize)!/UInt32(MemoryLayout<Float32>.stride)) 

    for input in 0 ..< blI!.count{ 

     let bI = blI?[input] 

     guard let inputData = bI?.mData else { 

      //assert(false) 

      return kAudioUnitErr_Uninitialized 
     } 

     let samplesBI = UnsafeMutablePointer<Float32>(inputData.assumingMemoryBound(to: Float32.self)) 

     let samplesI = UnsafeMutableBufferPointer<Float32>(start: samplesBI, count: numSamples) 

     for sampleIndex in 0 ..< samplesI.count { 

      samplesI[sampleIndex] *= 0.5 
     } 

    } 

    return noErr 
} 

什么会导致获取和设置的这个低效行为指针数据？由于它正在处理音频样本，因此效率低下会导致音频信号中出现断断续续的情况。

Answer 1

可以跳过UnsafeMutableBufferPointer（）调用，和索引直接样品指针：

let bufferListPtr = UnsafeMutableAudioBufferListPointer(ioData) 
... 
let mBuffer : AudioBuffer = bufferListPtr[0] 
let count = Int(mBuffer.mDataByteSize)/yourSampleSizeInBytes 
let dataPointer = UnsafeMutableRawPointer(mBuffer.mData) 
if let dptr = dataPointer { 
    let sampleArray = dptr.assumingMemoryBound(to: yourSampleType.self) 
    for i in 0..<(count) { 
     let x = sampleArray[i] 
     let y = myModifySample(x) 
     sampleArray[i] = y 
    } 
} 

我使用的Int16为mySampleType（大小= 2个字节），但它应该为4个字节的类型浮动工作，以及。

直接使用原始内存指针可能会避免一些缓冲区getter/setter效率低下（也需要验证，所以要小心！）。