A few weeks ago Den Raskovalov and I had a fancy conversation on C## performance, which turned into a tiny but fun coding exercise. The statement to prove or disprove was:

“The C++ code listed below, being translated to C#, will never be close to C++ in terms of speed.”

auto computeSum(char* fileName) {
	    auto fIn = open(fileName, O_RDONLY | O_BINARY, 0644);

	    static constexpr size_t BUFFER_SIZE = 1 << 16;
	    uint8_t buffer[BUFFER_SIZE];
	    uint8_t const* pBuffer = nullptr;
	    size_t bufferPos = 0;
	    size_t bufferLen = 0;

	    int64_t sum = 0;
	    uint8_t b;
	    int n = 0;
	    while (bufferLen = read(fIn, buffer, BUFFER_SIZE)) {
	        pBuffer = buffer;
	        const uint8_t* const pBufferEnd = buffer + bufferLen;
	        while (pBuffer != pBufferEnd) {
	            if (*pBuffer < 128) {
	                n = (n << 7) + *pBuffer;
	            } else {
	                n = (n << 7) + *pBuffer - 128;
	                sum += n;
	                n = 0;
	            }
	            ++pBuffer;
	        }
	    }
	    close(fIn);
	    return sum;
	}

#avx #dot-net-core #simd #c-sharp-programming #programming