Calculate Download / Upload Speed ASIHTTPRequest

Question

I am downloading / uploading a few files with some progress tracking. All with the help of ASIHTTP

Currently I get progress of the task at some intervals, providing me the bytes downloaded. I wish to know how to get the download speed from this.

As per what I have read and thought it should be something like

while starting download, keep the start time and bytesOfDownloading

NSTimeInterval time1 = [[NSDate date] timeIntervalSince1970];
unsigned long long bytesOfDownloading1 = 0;

When you get the first process callback for progress You can get

NSTimeInterval time2 = [[NSDate date] timeIntervalSince1970];
unsigned long long bytesOfDownloading2 = bytesOfDownloading;

NSInteger timeDiff = (time2 - time1);
double transfer_rate = (bytesOfDownloading2 - bytesOfDownloading1) / timeDiff;

And keep new state

time1 = time2;
bytesOfDownload1 = bytesOfDownload2;

But my question is is there a way in which ASIHTTP or any other USURL related library directly gives me the transfer rate, without need for all such calculations

Thanks