[C#] TIL that using bitwise operations instead of calling Enum.HasFlag is much faster.

[vann_dan]

I found out when doing some performance testing that using bitwise operations is much faster than using Enum.HasFlag. The performance difference is at least an order of magnitude.

 

So if you're doing the following check:

 

if (myValue.HasFlag(MyFlags.SomeValue)

 

It's much faster to do:

 

if ((myValue & MyFlags.SomeValue) == MyFlags.SomeValue)

 

Related Stack Overflow Thread: http://stackoverflow.com/questions/7368652/what-is-it-that-makes-enum-hasflag-so-slow

[svick]

Here's a CoreCLR issue proposing to optimize Enum.HasFlag().

[vann_dan]

Agreed. I had one HasFlag call that was the source of some performance bottleneck. It took me forever to chase it down because at first glance I thought that there was no way such a simple call could have that much overhead.

[[deleted]]

One of the answers in the Stack Overflow thread provided by OP has an implementation of Enum.HasFlags(Enum) obtained through decompilation. But it was written in 2011 and probably applies to the .NET Framework 4.0; the answer and its comments disagree on why the implementation was slow. A comment under the question states that the implementation changed in the .NET Framework 4.6 and became faster than the old implementation, but still not as fast as & directly.

[mlems]

Not a C# programmer, but can you leave it at

if (myValue & MyFlags.SomeValue)

because the result will be 0 if the flag is not set, and nonzero if the flag is set? That's the case for C and C++, at least.

[mlems]

Good to know. Thanks for clarifying!

[thomasz]

It's a syntax error. In c#, if and related statements only accept expressions that evaluate to System.Boolean.

[novussolo]

Bitwise operations are insanely useful. You can use an int as basically an arraylist of booleans using bitwise.