Passing a matrix from C to Haskell

I need to pass a big 2-dimensional array of doubles from a legacy C code to a Haskell module. Of this huge array, the Haskell code will actually use only a few elements (say, 10 out of 100x20 matrix). Unfortunately, the C code does not know which data are actually needed in the Haskell module. What would be a good way to pass the array to Haskell and, once the data are handed over, what is the fastest way to fetch these elements? I was thinking of something like passing the array as Ptr Int#, but how do I fetch the elements that I am interested in? Cheers, Cyril