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Re: [PATCH] For RTEMS-LIBBSD support, add bitcount routines
- From: Craig Howland <howland at LGSInnovations dot com>
- To: <newlib at sourceware dot org>
- Date: Tue, 16 May 2017 15:04:58 -0400
- Subject: Re: [PATCH] For RTEMS-LIBBSD support, add bitcount routines
- Authentication-results: sourceware.org; auth=none
- References: <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