C# vs C - Big performance difference
You must be comparing debug builds. I just compiled your C code, and got
Time elapsed: 0.000000If you don't enable optimizations, any benchmarking you do is completely worthless. (And if you do enable optimizations, the loop gets optimized away. So your benchmarking code is flawed too. You need to force it to run the loop, usually by summing up the result or similar, and printing it out at the end)
It seems that what you're measuring is basically "which compiler inserts the most debugging overhead". And turns out the answer is C. But that doesn't tell us which program is fastest. Because when you want speed, you enable optimizations.
By the way, you'll save yourself a lot of headaches in the long run if you abandon any notion of languages being "faster" than each others. C# no more has a speed than English does.
There are certain things in the C language that would be efficient even in a naive non-optimizing compiler, and there are others that relies heavily on a compiler to optimize everything away. And of course, the same goes for C# or any other language.
The execution speed is determined by:
- the platform you're running on (OS, hardware, other software running on the system)
- the compiler
- your source code
A good C# compiler will yield efficient code. A bad C compiler will generate slow code. What about a C compiler which generated C# code, which you could then run through a C# compiler? How fast would that run? Languages don't have a speed. Your code does.
I'll keep it brief, it is already marked answered. C# has the great advantage of having a well defined floating point model. That just happens to match the native operation mode of the FPU and SSE instruction set on x86 and x64 processors. No coincidence there. The JITter compiles Math.Sqrt() to a few inline instructions.
Native C/C++ is saddled with years of backwards compatibility. The /fp:precise, /fp:fast and /fp:strict compile options are the most visible. Accordingly, it must call a CRT function that implements sqrt() and checks the selected floating point options to adjust the result. That's slow.
Since you never use 'root', the compiler may have been removing the call to optimize your method.
You could try to accumulate the square root values into an accumulator, print it out at the end of the method, and see what's going on.
Edit : see Jalf's answer below