memcpy(from:ptr, to:ptr, n:size) | effects [read from[0:n], write to[0:n]]

reverse_half(s:string):string | effects [read s.buffer[0:s.length]]
	size n = s.length
	copy = new string(n)
    m = n - n / 2
	memcpy(copy.buffer, s.buffer + m, n/2)
	memcpy(copy.buffer + m, s.buffer, m)
	return copy