Junio C Hamano <gitster@xxxxxxxxx> writes:
> I wonder if the approach like the following might be cleaner to
> extend as we find other oddball platforms.
>
> #undef __SHA1DC_BYTE_ORDER
> #if defined(_BYTE_ORDER)
> #define __SHA1DC_BYTE_ORDER _BYTE_ORDER
> #elif defined(__BYTE_ORDER)
> #define __SHA1DC_BYTE_ORDER __BYTE_ORDER
> #elif defined(__BYTE_ORDER__))
> #define __SHA1DC_BYTE_ORDER __BYTE_ORDER__
> #endif
>
> #ifdef __SHA1DC_BYTE_ORDER
> #undef __SHA1DC_BIG_ENDIAN
> /* do the same for variations of BIG_ENDIAN constant */
> #if defined(_BIG_ENDIAN)
> ...
> #endif
>
> #if __SHA1DC_BYTE_ORDER == __SHA1DC_BIG_ENDIAN
> #define SHA1DC_BIGENDIAN
> #endif
> #else
> /*
> * as the platform does not use "compare BYTE-ORDER with
> * BIG_ENDIAN macro" strategy, defined-ness of BIG_ENDIAN
> * may be usable as a sign that it is a big-endian box.
> */
> #endif
IF the above turns out to be a good approach, it may be better to
determine the __SHA1DC_BIG_ENDIAN outside #ifdef __SHA1DC_BYTE_ORDER
block. That makes the resulting #if/#endif nest shallower; the last
part for platforms that uses defined-ness of BIG_ENDIAN (with
underscore variants) needs to know __SHA1DC_BYTE_ORDER anyway.
So in short, two preparatory blocks followed by the real thing,
something along the lines of...
#undef __SHA1DC_BYTE_ORDER
/* set the above from BYTE_ORDER with underscore */
#undef __SHA1DC_BIG_ENDIAN
/* set the above from BIG_ENDIAN with underscore */
#undef SHA1DC_BIGENDIAN
#if defined(__SHA1DC_BYTE_ORDER)
# if defined(__SHA1DC_BIG_ENDIAN)
# if __SHA1DC_BYTE_ORDER == __SHA1DC_BIG_ENDIAN
# define SHA1DC_BIGENDIAN
# endif
# endif
#else
/* other heuristics like processor bits here */
/*
* the platform does not compare BYTE-ORDER with BIG-ENDIAN
* so take the definedness of BIG-ENDIAN as the sign that
* the box is big endian.
*/
# if defined(__SHA1DC_BIG_ENDIAN)
# define SHA1DC_BIGENDIAN
# endif
#endif
