svn commit: r232266 - in head/sys: amd64/include i386/include
dim at FreeBSD.org
Tue Feb 28 20:56:01 UTC 2012
On 2012-02-28 20:39, Tijl Coosemans wrote:
> Author: tijl
> Date: Tue Feb 28 19:39:54 2012
> New Revision: 232266
> URL: http://svn.freebsd.org/changeset/base/232266
> Copy amd64 endian.h to x86 and merge with i386 endian.h. Replace
> amd64/i386/pc98 endian.h with stubs.
> In __bswap64_const(x) the conflict between 0xffUL and 0xffULL has been
> resolved by reimplementing the macro in terms of __bswap32(x). As a side
> effect __bswap64_var(x) is now implemented using two bswap instructions on
> i386 and should be much faster. __bswap32_const(x) has been reimplemented
> in terms of __bswap16(x) for consistency.
> +#define __bswap32_const(_x) \
> + (((__uint32_t)__bswap16(_x) << 16) | __bswap16((_x) >> 16))
> +#define __bswap32(_x) \
> + (__builtin_constant_p(_x) ? \
> + __bswap32_const((__uint32_t)(_x)) : __bswap32_var(_x))
> +#define __bswap64_const(_x) \
> + (((__uint64_t)__bswap32(_x) << 32) | __bswap32((_x) >> 32))
Hmm, shouldn't __bswap32_const() be implemented in terms of
__bswap16_const(), and similarly for __bswap64_const(), which should be
implemented in terms of __bswap32_const()?
The whole reason for the difficult dance with __builtin_constant_p is to
allow for compile-time resolving of bswap'd constants. Invoking the
regular __bswap() macros doesn't gain you anything here.
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