And, apart from a stray use of new and delete, this looks almost like valid C99 code to me. Not that that diminishes the achievement any, of course. I'd quibble mildly about his choice of compile flags and make some minor stylistic changes to the code (like the tacky transpose :), but I don't think it would affect the benchmark results any.

Given the code used, it looks like it might be straightforward to use openmp rather than pthreads. I'd be interested in seeing how that works out.