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From: Thomas Monjalon <thomas.monjalon@6wind.com>
To: "Qiu, Michael" <michael.qiu@intel.com>
Date: Thu, 04 Dec 2014 10:00:09 +0100
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Cc: dev@dpdk.org, Chao Zhu <chaozhu@linux.vnet.ibm.com>
Subject: Re: [dpdk-dev] [PATCH 1/2] eal: detect endianness
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2014-12-04 02:28, Qiu, Michael:
> On 12/4/2014 5:26 AM, Thomas Monjalon wrote:
> > There is no standard to check endianness.
> > So we need to try different checks.
> > Previous trials were done in testpmd (see commits
> > 51f694dd40f56 and 64741f237cf29) without full success.
> > This one is not guaranteed to work everywhere so it could
> > evolve when exceptions are found.
[...]
> >  #include <stdint.h>
> > +#ifdef RTE_EXEC_ENV_BSDAPP
> > +#include <sys/endian.h>
> > +#else
> > +#include <endian.h>
> > +#endif
> > +
> > +/*
> > + * Compile-time endianness detection
> > + */
> > +#define RTE_BIG_ENDIAN    1
> > +#define RTE_LITTLE_ENDIAN 2
> > +#if defined __BYTE_ORDER
> > +#if __BYTE_ORDER == __BIG_ENDIAN
> > +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
> > +#elif __BYTE_ORDER == __LITTLE_ENDIAN
> > +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
> > +#endif /* __BYTE_ORDER */
> > +#elif defined __BYTE_ORDER__
> > +#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
> > +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
> > +#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
> > +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
> > +#endif /* __BYTE_ORDER__ */
> > +#elif defined __BIG_ENDIAN__
> > +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
> > +#elif defined __LITTLE_ENDIAN__
> > +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
> > +#endif
> 
> What do you think about :
> 
> +/*
> +  * Compile-time endianness detection
> + */
> +#define RTE_BIG_ENDIAN 1
> +#define RTE_LITTLE_ENDIAN 2
> +if defined __BYTE_ORDER__    /* Prefer gcc build-in macros */
> +#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
> +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
> +#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
> +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
> +#endif /* __BYTE_ORDER__ */
> +#else
> +#if defined RTE_EXEC_ENV_BSDAPP
> +#include <sys/endian.h>
> +#else
> +#include <endian.h>
> +#endif
> +#if defined __BYTE_ORDER
> +#if __BYTE_ORDER == __BIG_ENDIAN
> +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
> +#elif __BYTE_ORDER == __LITTLE_ENDIAN
> +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
> +#endif /* __BYTE_ORDER */
> +#elif defined __BIG_ENDIAN__
> +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
> +#elif defined __LITTLE_ENDIAN__
> +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
> +#endif
> +#endif

Please, could you give more explanations about your proposal?
Why not always try to include endian.h?
Why giving high priority to __BYTE_ORDER__?

-- 
Thomas