typedef struct int64_struct {
unsigned int lo;
unsigned int hi;
} int64;

void add_64(int64 *dest, int64 *src1, int64 *src2)
{ unsigned hibit1=src1->lo >> 31, hibit2=src2->lo >> 31, hibit3;

  dest->lo=src1->lo + src2->lo;
  hibit3=dest->lo >> 31;

  // hier geht man anscheinend davon aus, dass src1.lo > src2.lo ???
  dest->hi=src1->hi + src2->hi + ((hibit1 & hibit2) || (hibit1 != hibit3));
  return;
}

int main(void) {

int64 dest;
int64 summand1;
int64 summand2;

summand2.lo = 0xF0000001;
summand2.hi = 0x00000000;

summand1.lo = 0x30000002;
summand1.hi = 0x00000000;
add_64(&dest, &summand1, &summand2);
}