Atomically load a value and replace it with that value minus the
using standard pointer arithmetic rules, and return the old value.
T* fetch_sub( ptrdiff_t i, memory_order order = memory_order_seq_cst) volatile;
Atomically retrieves the existing value of
*this and stores old-value
The value of
*this immediately prior to the
This is an atomic read-modify-write operation for the memory