modernc.org/ccgo/v3@v3.16.14/lib/testdata/gcc-9.1.0/gcc/testsuite/gcc.c-torture/execute/20110418-1.c (about)

     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