1  typedef unsigned long long uint64_t;
       2  void f(uint64_t *a, uint64_t aa) __attribute__((noinline));
       3  void f(uint64_t *a, uint64_t aa)
       4  {
       5    uint64_t new_value = aa;
       6    uint64_t old_value = *a;
       7    int bit_size = 32;
       8      uint64_t mask = (uint64_t)(unsigned)(-1);
       9      uint64_t tmp = old_value & mask;
      10      new_value &= mask;
      11      /* On overflow we need to add 1 in the upper bits */
      12      if (tmp > new_value)
      13          new_value += 1ull<<bit_size;
      14      /* Add in the upper bits from the old value */
      15      new_value += old_value & ~mask;
      16      *a = new_value;
      17  }
      18  int main(void)
      19  {
      20    uint64_t value, new_value, old_value;
      21    value = 0x100000001;
      22    old_value = value;
      23    new_value = (value+1)&(uint64_t)(unsigned)(-1);
      24    f(&value, new_value);
      25    if (value != old_value+1)
      26      __builtin_abort ();
      27    return 0;
      28  }
      29