(Example program with "strange" output:)

 > % cat xxx.c
 > /* */
 > #include <stdio.h>
 > 
 > long	b = 1 << 24;
 > u_long	c = 1 << 9;
 > int	d;
 > 
 > void
 > f(off_t a)
 > {
 > 	printf("a=0x%016qx\n", a);
 > }
 > 
 > int
 > main()
 > {
 > 	for(d = 1; d >= -1; d -= 2) {
 > 		f(b * c + d);
 > 		f((off_t)(b * c + d));
 > 		f((off_t)b * c + d);
 > 		f(b * (off_t)c + d);
 > 		f(b * c + (off_t)d);
 > 	}
 > 	return (0);
 > }
 > % cc xxx.c
 > % ./a.out
 > a=0x0000000000000001
 > a=0x0000000000000001
 > a=0x0000000200000001
 > a=0x0000000200000001
 > a=0x0000000000000001
 > a=0x00000000ffffffff
 > a=0x00000000ffffffff
 > a=0x00000001ffffffff
 > a=0x00000001ffffffff
 > a=0xffffffffffffffff

Yes.  Welcome to the wonderful world of Ansi C integral promotions.
This is entirely correct and the expected result.
Not exactly *intuitive*, mind you, but nevertheless right.  Any Ansi
C compiler should give the same results, and I just tried Sun, SGI,
and DEC with the same results.

  -  Arne H. J.