Fastest way to replace multiple strings in a huge string

Question

I m looking for the fastest way to replace multiple (~500) substrings of a big (~1mb) string. Whatever I have tried it seems that String.Replace is the fastest way of doing

Answer 1

As I were mildly interested in this problem, I crafted few solutions. With hardcore optimizations it's possible to go down even more.

To get the latest source: https://github.com/ChrisEelmaa/StackOverflow/blob/master/FastReplacer.cs

And the output

-------------------------------------------------------
| Implementation       | Average | Separate runs      |
|----------------------+---------+--------------------|
| Simple               |    3485 | 9002, 4497, 443, 0 |
| SimpleParallel       |    1298 | 3440, 1606, 146, 0 |
| ParallelSubstring    |     470 | 1259, 558, 64, 0   |
| Fredou unsafe        |     356 | 953, 431, 41, 0    |
| Unsafe+unmanaged_mem |      92 | 229, 114, 18, 8    |
-------------------------------------------------------

You won't probably beat the .NET guys in crafting your own replace method, it's most likely already using unsafe. I do believe you can get it down by factor of two if you write it completely in C.

My implementations might be buggy, but you can get the general idea.