C move memory parts inplace

Question

I am implementing several datastructures and one primitive I want to use is the following: I have a memory chunk A[N] (it has a variable length, but I take 100 for my examples)

Answer 1

This solution is O(N) and uses already processed source locations as scratch space to use when ranges overlap. It will swap contents of source and destination up to the point when it reaches the start of destination, then it will proceed copying from the scratch space generated before. The second loop restores the clobbered region after each character of the scratch space is used.

move(A,N, src_idx, dst_idx, len)
{
  first_dst_idx=dst_idx;
  first_src_idx=src_idx;
  mlen=0;
  while(src_idx != first_dst_idx && len > 0)
  {
    temp = A[dst_idx];
    A[dst_idx] = A[src_idx];
    A[src_idx] = temp;
    src_idx=(src_idx+1) mod N;
    dst_idx=(dst_idx+1) mod N;
    len--; mlen++;
  }
  src_idx = first_src_idx;
  while(len > 0)
  {
    A[dst_idx] = A[src_idx];
    A[src_idx] = A[first_dst_idx];
    src_idx=(src_idx+1) mod N;
    dst_idx=(dst_idx+1) mod N; 
    first_dst_idx=(first_dst_idx+1) mod N;
    len--;
  }
  while(mlen > 0)
  { // restore reamining scratch space
    A[src_idx] = A[first_dst_idx];
    src_idx=(src_idx+1) mod N;
    first_dst_idx=(first_dst_idx+1) mod N;
    mlen--;
  }
}