How do realloc and memcpy work?

Question

I have two questions.

1. Do realloc() and memcpy() copy the entries in an array to another in a way faster than just iterating on eac

Answer 1

1. It can be conjectured that memcpy could be written such that it would move large number of bits around. e.g. It's entirely possible to copy the data using SSE instructions, if it is advantageous.

As other said, it won't be faster than O(n), but memory systems often have a preferred block size, and also it's possible to, say, write the size of a cache line at a time.