Reading file with "gaps" in destination array

Question

I'm trying to find a way to read a file into an array with "gaps":
So the read data is in the byte array buffer at the positions buffer[0], buffer[2], .., buffer[2*i], without any significant speed loss.

More specifically I want to read it int-wise (i.e. b[0], b[4], ..., b[i * 4]).

Is that in any way possible (C#, C++) or should I look for another approach?

A bit more background:
I'm trying to speed up a hash algorithm (hashes the file blockwise, concats blockhashes, hashes it, and takes the resulting hash).
The idea is/was to take SSE3 and do 4 blocks in "parallel", which is why I need the data in that way, so I can easily load the data into the registers.

The (pinvokable) lib I wrote in C++ gives nice results (i.e. 4 times as fast), but reordering the data eats up the speed gains.

Currently I'm reading the file blockwise and then reorder the ints (C#):

unsafe {
    uint* b = (uint*)buffer.ToPointer() + chunkIndex;
    fixed(byte* blockPtr = chunk) {
        uint* blockIntPtr = (uint*)blockPtr;

        for(int i = 0; i < 9500 * 1024 / 4; i += 4) {
            *(b + 00) = blockIntPtr[i + 0];
            *(b + 04) = blockIntPtr[i + 1];
            *(b + 08) = blockIntPtr[i + 2];
            *(b + 12) = blockIntPtr[i + 3];
            b += 16;
        }
    }
}

chunk is a byte array and chunkIndex is an int, passed as methods parameters.
buffer is a uint32_t* pointer which is allocated by my C++ code.

The problem with this is that it takes too long. Calling the above code 4 times takes around 90ms while the hashing takes 3ms.
The big discrepancy strikes me as a bit odd, but it produces correct hashes.

Answer 1

in c++ I would do something like:

uint* b = (uint*)buffer;
 for(int i = 0; i < 9500 * 1024; i ++) {
       //read 4 ints
            *(b+i+0)  = blockIntPtr[i + 0];
            *(b+i+1)  = blockIntPtr[i + 1];
            *(b+i+2)  = blockIntPtr[i + 2];
            *(b+i+3)  = blockIntPtr[i + 3];
      //skip next 12 ints
            b += 16;
   }