Obviously, I could just use a for-loop. But then my code is theoretically
telling the system to XOR each byte individually, wasting most of the CPU on
each instruction.
I wrote unsafe code to do this with 32-bit and 64-bit int pointers.
Surprisingly they both performed about the same (I guess, at least on my
system, 64bit instructions take longer to execute, effectively eliminating most
of the gains of the wider bus). Unsurprisingly, they greatly outperformed the
unoptimized for-loop.
Surprisingly, the difference between the optimized unsafe code and the
optimized for-loop suggested it was a waste of effort. (Only marginally
faster.)
I don't know what kind of optimizations the compilers are able to perform on
this code:
for (int i=0; i<buf1.Length; i++) {
buf2[i] = (byte)(buf1[i] ^ buf2[i]);
}
I am surprised if that optimizes so well as to literally make it a waste of
time to pursue anything better. But if someone here says so, I'll have to
believe you.
I haven't benchmarked, but rumor on the internet suggests that the for-loop for
copying bytes from one buffer to another is slow compared to Array.Copy, which
is slower still than Buffer.BlockCopy. Assuming this is correct, I have to
assume it's possible to have an optimized method of XOR'ing blocks of data too.
But I haven't found any such method in .Net.
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