PiBenchmark
The source code is very simple and easy to understand!
About:
Benchmark CPU of android device by calculating Pi number
Version: 1.4
Copyright 2014 Navid Norouzi -- Iran
GNU General Public License
How we calculate Pi:
tan 45° (or π/4 radians) =1, therefore
arctan(1) = π/4
and if we plug this into Gregory's Series: arctan(t) = t-(t^3/3)+(t^5/5)-(t^7/7)+(t^9/9)-... we get the following surprisingly simple and beautiful formula for π:
arctan(1) = π/4 = 1-(1/3)+(1/5)-(1/7)+(1/9) - ...