c - can realloc move pointer if new size smaller?

Question

I am wondering whether the C or C++ standard guarantees that a pointer is not changed when realloc is called with a smaller (nonzero) size:

size_t n=1000;
T*ptr=(T*)malloc(n*sizeof(T));
//<--do something useful (that won't touch/reallocate ptr of course)
size_t n2=100;//or any value in [1,n-1]
T*ptr2=(T*)realloc(ptr,n2*sizeof(T));
//<-- are we guaranteed that ptr2==ptr ?

Basically, can the OS decide on its own that since we freed a large memory block, he wants to take advantage of all reallocs to defragment the memory, and somehow move ptr2 ?

Answer 1

http://opengroup.org/onlinepubs/007908775/xsh/realloc.html

Upon successful completion with a size not equal to 0, realloc() returns a pointer to the (possibly moved) allocated space.

Nope, no guarantee