timeBlock.swift

import Darwin
// import Darwin.Mach.mach_time   // (mach_timebase_info, mach_absolute_time)
// import Darwin.Mach.clock_types // (NSEC_PER_*)
public func timeBlockNSec(block: ()->()) -> Double { // in nanoseconds
  var info = mach_timebase_info(numer: 0, denom: 0)
  let kr = mach_timebase_info(&info)
  if kr != KERN_SUCCESS {
    fatalError("Initialization of `mach_timebase_info` failed with code \(kr).")
  }
  if info.denom == 0 {
    fatalError("Initialized `mach_timebase_info` contains invalid value.")
  }
  
  let scale = Double(info.numer)/Double(info.denom)
  
  let start = mach_absolute_time()
  block()
  let end = mach_absolute_time()
  let delta = Double(end - start)
  return delta * scale
}

public func timeBlockUSec(block: ()->()) -> Double { // in microseconds
  return timeBlockNSec(block)/Double(NSEC_PER_USEC)
}

public func timeBlockMSec(block: ()->()) -> Double { // in milliseconds
  return timeBlockNSec(block)/Double(NSEC_PER_MSEC)
}

public func timeBlock(block: ()->()) -> Double { // in seconds
  return timeBlockNSec(block)/Double(NSEC_PER_SEC)
}

// Resources:
// http://www.bignerdranch.com/blog/a-timing-utility/
// https://gist.github.com/bignerdranch/2006587
// https://developer.apple.com/library/mac/qa/qa1398/_index.html
// https://developer.apple.com/library/ios/qa/qa1643/_index.html
// https://developer.apple.com/library/mac/samplecode/CoreAudioUtilityClasses/Listings/CoreAudio_PublicUtility_CAHostTimeBase_cpp.html
// ClockFrequency: (Double(info.numer)/Double(info.denom)) * Double(NSEC_PER_SEC)