Amplify audiobuffer xcode ios

Question

I have AudioBuffer as shown below. It can play through the speaker. I would like to know a way to amplify those buffer before I play. How shall I modify?

/**
 This callback is called when the audioUnit needs new data to play through the
 speakers. If you don't have any, just don't write anything in the buffers
*/
static OSStatus playbackCallback(void *inRefCon, 
                             AudioUnitRenderActionFlags *ioActionFlags, 
                             const AudioTimeStamp *inTimeStamp, 
                             UInt32 inBusNumber, 
                             UInt32 inNumberFrames, 
                             AudioBufferList *ioData) {    
// Notes: ioData contains buffers (may be more than one!)
// Fill them up as much as you can. Remember to set the size value in each buffer to match how
// much data is in the buffer.


for (int i=0; i < ioData->mNumberBuffers; i++) { // in practice we will only ever have 1 buffer, since audio format is mono




    AudioBuffer buffer = ioData->mBuffers[i];


  //        NSLog(@"  Buffer %d has %d channels and wants %d bytes of data.", i, buffer.mNumberChannels, buffer.mDataByteSize);

    // copy temporary buffer data to output buffer
    UInt32 size = min(buffer.mDataByteSize, [iosAudio tempBuffer].mDataByteSize); // dont copy more data then we have, or then fits
    memcpy(buffer.mData, [iosAudio tempBuffer].mData, size);
    buffer.mDataByteSize = size; // indicate how much data we wrote in the buffer

    // uncomment to hear random noise
    /*
    UInt16 *frameBuffer = buffer.mData;
    for (int j = 0; j < inNumberFrames; j++) {
        frameBuffer[j] = rand();
    }
    */

}

return noErr;
}