really, between 3 & 4, about 3.6-3.7... Book provides introduction into OpenCL, basic concepts, structures, functions, etc. But some topics aren't covered in much details
This is a very good book. There is a problem with it, though: The canonical example of OpenCL is bitonic sort. The bitonic sort code in the book is given with almost no comment. The author gives a good explanation of the bitonic sort, but never tells which part of the algorithm corresponds to what block in the code.. I havent read the last chapter on combining OpenCl and OpenGL, which seems to be very interesting..
By reading this book, I got a lot of insights on the internal architecture of modern GPU's.