Re: [avr-gcc-list] AVR Libc int32_t and uint32_t typedefs are incorrect

[Georg-Johann Lay]

Joerg Wunsch schrieb:
> "Paul McClean" <address@hidden> wrote:
>
> The standard C does not make *any* claim about the actual number of
> bits in an `unsigned long' data type, it only specifies a *minimum*
> number of bits (indirectly, by telling a minimal magnitude value for
> LONG_MIN, LONG_MAX, and ULONG_MIN, respectively).  Thus, an `unsigned

The C standard says it is implementation defined.

The implementation (AVR backend of GCC) say: long is 32 bits or 16 bits 
if -mint8 is on.

As avr-libc is only intended to work together with GCC, avr-libc could 
use built-in macros:

typedef __INT32_TYPE__ int32_t;

or

But for static analysis and checking there is more information exposed 
by defining like so:

#if __SIZEOF_INT__ == 2
typedef signed long int32_t;
#elif __SIZEOF_INT__ 1
/* -mint8 is on */
typedef signed long long int32_t;
#else
#error ...
#endif

or so:

#if defined (__SIZEOF_LONG__) && __SIZEOF_LONG__ == 4
typedef signed long int32_t;
#elif defined (__SIZEOF_LONG_LONG__) && __SIZEOF_LONG_LONG__ == 4
typedef signed long long int32_t;
#else
#error ...
#endif

As fas as I know the only reason why avr-libc used mode attribute is to 
factor out impact of -mint8, but the same can be achived by testing 
__SIZEOF_INT__. Unfortunately, thr writer of -mint8 did not define 
respective built-in macro like __AVR_MINT8__, but __SIZEOF_INT__ can 
serve the same purpose.

> long' datatype could as well have 64 bits, still conforming to the
> standard.  Likewise, an `unsigned int' on many GCC targets is 32 bits
> long, so why does your tool assume it were 16 bits?
>
> Moreover, how would your tool handle Johann's recent GCC addition of a
> 24-bit integer type?  This one can only be expressed by relying on the
> definition of __int24_t (or __uint24_t) providing the necessary magic
> to tell this to the compiler.

Notice that the names are __int24 and __uint24 similar to __int128 types 
some backend support. avr-gcc does *not* typedef/define int24_t or 
uint24_t because it's no good to mess in user name space. But if user 
likes he still can

#ifdef __INT24_MAX__
typedef __int24 int24_t;
#else
/* fallback on 32-bit integers */
typedef int32_t int24_t;

Johann