Re: [avr-gcc-list] I Think This Is A Bug

[Curtis Maloney]

David Kelly wrote:
> Avr-gcc doesn't doesn't fully evaluate this expression which should
> reduce to 113. The FreeBSD version of gcc has no problem, but both the
> FreeBSD ports version of avr-gcc and current WinAVR avr-gcc behave
> identially (wrongly) the same:

Hello, and welcome to the world of "Not everyone uses 32bit ints.".  AVR ints 
are 16bit.  Pay attention to the warnings.  Warnings are your friends.

> unsigned long ulval;
> unsigned char ucval;
>
> junk()
> {
>         ucval = (1+(7372800L/(256*256)));
>         ulval = (1+(7372800L/(256*256)));
> }

GCC is seeing 256 * 256, as the integer multiplication of two 16bit values. 
0x100 * 0x100 = 0x10000... oops, that won't fit into 16bits!  And thus, the 
overflow warnings you see here:

> junk.c:6: warning: integer overflow in expression
> junk.c:6: warning: integer overflow in expression
> junk.c:6: warning: large integer implicitly truncated to unsigned type
> junk.c:7: warning: integer overflow in expression
> junk.c:7: warning: integer overflow in expression

Solution?  Mark the 256s as Longs, and see how it goes.

--
Curtis Maloney
address@hidden