title: How to round down an address in C?
body: <p>Say I had a char* ptr with address of 0x7fffaf6aa87f, How can I round that down to a multiple of 8 so that it would be 0x7fffaf6aa878?</p>
  <p>or if it was 0x7fffaf6aa875, it would get rounded down to 0x7fffaf6aa870.</p>