From: Craig Howland <howland@LGSInnovations.com>
To: <newlib@sourceware.org>
Subject: Re: [PATCH] For RTEMS-LIBBSD support, add bitcount routines
Date: Tue, 16 May 2017 19:05:00 -0000 [thread overview]
Message-ID: <e49202b4-8eec-af40-535d-8f9ca56bf4a8@LGSInnovations.com> (raw)
In-Reply-To: <201705161823.v4GIMc16015657@mx0a-00116901.pphosted.com>
On 05/16/2017 02:23 PM, Kevin Kirspel wrote:
> ---
> newlib/libc/include/sys/types.h | 66 ++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 62 insertions(+), 4 deletions(-)
>
> diff --git a/newlib/libc/include/sys/types.h b/newlib/libc/include/sys/types.h
> index 65ff520..83f891e 100644
> ...
> +#ifdef __LP64__
> +static __inline __uint64_t
> +__bitcount64(__uint64_t _x)
> +{
> ...
> +}
> +
> +#define __bitcountl(x) __bitcount64((unsigned long)(x))
> +#else /* __LP64__ */
> +static __inline __uint64_t
> +__bitcount64(__uint64_t _x)
> +{
> + return (__bitcount32(_x >> 32) + __bitcount32(_x));
> +}
> +
> +#define __bitcountl(x) __bitcount32((unsigned long)(x))
> +#endif /* __LP64__ */
> +#define __bitcount(x) __bitcount32((unsigned int)(x))
> +#endif /* __POPCNT__ */
> +
Depending only upon LP64 is not sufficient in general to get all the sizes
right. (ARM Cortex A53, for example, has 64-bit int, too--ILP64. So A53 would
probably end up with two problems, bitcountl and bitcount.)
One possible solution would be something similar to this size-agnostic endian
function I use:
#define __bswap(x) \
__builtin_choose_expr( \
sizeof(x) == sizeof(char), \
(x), \
__builtin_choose_expr( \
sizeof(x) == sizeof(short), \
__bswap16(x), \
__builtin_choose_expr( \
sizeof(x) == sizeof(int), \
__bswap32(x), \
__builtin_choose_expr( \
sizeof(x) == sizeof(long long), \
__bswap64(x), \
/* The void expression results in a compile-time error \
when assigning the result to something. */ \
(void) 0 \
) \
) \
) \
)
One problem with it is that it is GCC-specific with the use of
__builtin_choose_expr(), but that can be avoided, too, by using a contruct
similar to that for fpclassify in math.h (use sizeof(int)==4 and sizeof(int)==8
for the tests, etc.)--the version in the else when the GNUC_PREREQ(4,4) check fails.
Craig
next prev parent reply other threads:[~2017-05-16 19:05 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-16 18:23 Kevin Kirspel
2017-05-16 19:05 ` Craig Howland [this message]
2017-05-17 5:22 ` Sebastian Huber
2017-05-17 5:11 ` Sebastian Huber
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