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From: Bruce Evans <bde@zeta.org.au>
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To: Nate Lawson <nate@root.org>
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cc: David O'Brien <obrien@FreeBSD.org>
cc: Ruslan Ermilov <ru@FreeBSD.org>
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cc: Mike Barcroft <mike@FreeBSD.org>
Subject: Re: cvs commit: src/sys/sys endian.h src/share/man/man9 byteorder.9
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On Fri, 4 Apr 2003, Nate Lawson wrote:

> On Fri, 4 Apr 2003, Ruslan Ermilov wrote:
> > +#define	BSWAP16(x)	(uint16_t) \
> > +	(((x) >> 8) | ((x) << 8))
> > +
> > +#define	BSWAP32(x)	(uint32_t) \
> > +	(((x) >> 24) | (((x) >> 8) & 0xff00) | \
> > +	(((x) << 8) & 0xff0000) | ((x) << 24))

> I don't mind the addition of the macros but I don't like the
> implementation.  Too many unnecessary casts and overly complicated.

I fear it has not enough necessary casts :-).  E.g., if x = (int16_t)0xfffe,
then on 32-bit machines sign extension gives 0xffffffff for BSWAP16(x).
Of course, BSWAP16()'s arg should be precisely uint16_t, but the function
interfaces don't require it to have the correct type except possibly on
non-2's complement machines where coercing the arg's type may cause
surprising changes to the arg's value.

Bruce