__extension__ union { double d; int i[2]; } u = { d: -0.25 };/* This assumes the endianness of words in a long long is the same as   that for doubles, which doesn't hold for a few platforms, but we   can probably special case them here, as appropriate.  */long long endianness_test = 1;#define MSW (*(int*)&endianness_test)intsignbit(double x){  __extension__ union { double d; int i[2]; } u = { d: x };  return u.i[MSW] < 0;}    int main(void){  if (2*sizeof(int) != sizeof(double) || u.i[MSW] >= 0)    exit(0);  if (!signbit(-0.25))    abort();  exit(0);}