Update: The below results are valid for the release version of RyuJIT in .NET Framework 4.6 without updates.
The challenge of the day: which method is faster?
public double Sqrt13()
{
return Math.Sqrt(1) + Math.Sqrt(2) + Math.Sqrt(3) + Math.Sqrt(4) + Math.Sqrt(5) +
Math.Sqrt(6) + Math.Sqrt(7) + Math.Sqrt(8) + Math.Sqrt(9) + Math.Sqrt(10) +
Math.Sqrt(11) + Math.Sqrt(12) + Math.Sqrt(13);
}
public double Sqrt14()
{
return Math.Sqrt(1) + Math.Sqrt(2) + Math.Sqrt(3) + Math.Sqrt(4) + Math.Sqrt(5) +
Math.Sqrt(6) + Math.Sqrt(7) + Math.Sqrt(8) + Math.Sqrt(9) + Math.Sqrt(10) +
Math.Sqrt(11) + Math.Sqrt(12) + Math.Sqrt(13) + Math.Sqrt(14);
}
I have measured the methods performance with help of BenchmarkDotNet for RyuJIT RC (a part of .NET Framework 4.6 RC) and received the following results:
// BenchmarkDotNet=v0.7.4.0
// OS=Microsoft Windows NT 6.2.9200.0
// Processor=Intel(R) Core(TM) i7-4702MQ CPU ＠ 2.20GHz, ProcessorCount=8
// CLR=MS.NET 4.0.30319.0, Arch=64-bit [RyuJIT]
Common: Type=Math_DoubleSqrtAvx Mode=Throughput Platform=X64 Jit=RyuJit .NET=Current
Method | AvrTime | StdDev | op/s |
------- |--------- |---------- |------------- |
Sqrt13 | 55.40 ns | 0.571 ns | 18050993.06 |
Sqrt14 | 1.43 ns | 0.0224 ns | 697125029.18 |
How so? If I add one more Math.Sqrt to the expression, the method starts work 40 times faster! Let's examine the situation..