Possible C compiler bug on 8086 machines

[Linus Torvalds]

In article <3577 at bruce.cs.monash.OZ.AU> alanf at bruce.cs.monash.OZ.AU (Alan Grant Finlay) writes:
>
>The following program demonstrates a printf that doesn't seem to work
>properly when compiled using a variety of C compilers for an 8086 machine.
>The program is as follows:
>-----------------------------//---------------------------
>
>#include <stdio.h>
>
>main()
>{
>   int x,y;
>   x = 65536/512;
>   y = 512;
>   printf("This works : %d, %d\n",x,y);
>   printf("This doesn't work : %d, %d\n",65536/512,512);
>}
>
>----------------------------//------------------------------
>
>And here is a sample output: 
>
>This works : 128, 512
>This doesn't work : 128, 0
>
>Does anyone have any idea why?
>Is this a problem with my machine or the printf routine?

This is NOT a bug, but a programming error :-). The 65536 is implicitly
converted to a long (ie 65536L), as it doesn't fit into a int on the
8086 (all 8086 c-compilers I've used use 16-bits ints, but on a 32 bit
int machine this works as "expected"). Thus 65536/512 is a LONG, not an
int and is sent to printf as such. The reason 'x=65536/512;printf(..,x,)
works is that 65536/512 is (implicitly) converted to an int by the
assignment into x.

The code works if you change the second printf to:

printf("%d %d",(int) (65536/512),512);	or alternately:
printf("%ld %d",65536/512,512);

NOTE! Please make 65536 EXPLICITLY long by using 65536L, this makes the
code much clearer and portable. (or don't use machines with a 16 bit int
:-)

		Linus "mostly wrong" Torvalds
		torvalds at cs.helsinki.fi