Re: [avr-libc-dev] RFC: avr/bits.h

[E. Weddington]

Bob Paddock wrote:

> On Tue, 01 Mar 2005 11:24:18 -0700, E. Weddington <address@hidden> 
> wrote:
>
>
>
> Is there any place where using this "((uint32_t)1<<(bitpos))"
> is going to generate real Flash occupying 32 bit code,
> when it is not needed?

Well, there's the tradeoff. Yes, it could if not used within the macros 
I proposed, if it used without typecasting.  I don't know if GCC is 
smart enough to catch it in all cases without the typecasting. For example:

#define bit(bitpos) ((uint32_t)1<<(bitpos))

PORTD |= bit(1);

The right hand side will be a 32 bit unsigned integer. The left side is 
an 8 bit unsigned value. Will GCC optimize correctly? What if the 
register is not in the IO space? What if the value on the left is not 
defined with volatile?

.......

After the previous discussion about this RFC (a while ago), I had some 
serious reservations about whether it should be implemented. Jörg has 
very good points in that the C language bit operators are an integral 
part of the language; a programmer should know how to use them. These 
macros *are* just another crutch, albeit sometimes useful. But it can't 
cover all cases, and it's no substitute for knowing the language. There 
will always be tradeoffs. And if someone is doing embedded work, it is 
practically a requirement that they know how to use these operators.

Eric