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Re: [PATCH v2] For RTEMS-LIBBSD support, add bitcount routines


On 17/05/17 15:06, Kevin Kirspel wrote:
---
  newlib/libc/sys/rtems/include/machine/types.h | 58 +++++++++++++++++++++++++++
  1 file changed, 58 insertions(+)

diff --git a/newlib/libc/sys/rtems/include/machine/types.h b/newlib/libc/sys/rtems/include/machine/types.h
index b28f923..0b0a100 100644
--- a/newlib/libc/sys/rtems/include/machine/types.h
+++ b/newlib/libc/sys/rtems/include/machine/types.h
@@ -83,3 +83,61 @@ typedef	__uintmax_t	rman_res_t;
  #endif
#endif /* __BSD_VISIBLE */
+
+#ifdef __POPCNT__
+#define	__bitcount64(x)	__builtin_popcountll((__uint64_t)(x))
+#define	__bitcount32(x)	__builtin_popcount((__uint32_t)(x))
+#define	__bitcount16(x)	__builtin_popcount((__uint16_t)(x))
+#define	__bitcountl(x)	__builtin_popcountl((unsigned long)(x))
+#define	__bitcount(x)	__builtin_popcount((unsigned int)(x))
+#else /* __POPCNT__ */
+/*
+ * Population count algorithm using SWAR approach
+ * - "SIMD Within A Register".
+ */
+static __inline __uint16_t
+__bitcount16(__uint16_t _x)
+{
+	_x = (_x & 0x5555) + ((_x & 0xaaaa) >> 1);
+	_x = (_x & 0x3333) + ((_x & 0xcccc) >> 2);
+	_x = (_x + (_x >> 4)) & 0x0f0f;
+	_x = (_x + (_x >> 8)) & 0x00ff;
+	return (_x);
+}
+
+static __inline __uint32_t
+__bitcount32(__uint32_t _x)
+{
+	_x = (_x & 0x55555555) + ((_x & 0xaaaaaaaa) >> 1);
+	_x = (_x & 0x33333333) + ((_x & 0xcccccccc) >> 2);
+	_x = (_x + (_x >> 4)) & 0x0f0f0f0f;
+	_x = (_x + (_x >> 8));
+	_x = (_x + (_x >> 16)) & 0x000000ff;
+	return (_x);
+}
+
+#if __SIZEOF_INT__ == 8
+static __inline __uint64_t
+__bitcount64(__uint64_t _x)
+{
+	_x = (_x & 0x5555555555555555) + ((_x & 0xaaaaaaaaaaaaaaaa) >> 1);
+	_x = (_x & 0x3333333333333333) + ((_x & 0xcccccccccccccccc) >> 2);
+	_x = (_x + (_x >> 4)) & 0x0f0f0f0f0f0f0f0f;
+	_x = (_x + (_x >> 8));
+	_x = (_x + (_x >> 16));
+	_x = (_x + (_x >> 32)) & 0x000000ff;
+	return (_x);
+}
+
+#define	__bitcountl(x)	__bitcount64((unsigned long)(x))
+#else /* __SIZEOF_INT__ == 8 */
+static __inline __uint64_t
+__bitcount64(__uint64_t _x)
+{
+	return (__bitcount32(_x >> 32) + __bitcount32(_x));
+}

The __bitcount64() implementation should be based on the word size of the architecture. Usually this is indicated by sizeof long.

+
+#define	__bitcountl(x)	__bitcount32((unsigned long)(x))
+#endif /* __SIZEOF_INT__ == 8 */
+#define	__bitcount(x)	__bitcount32((unsigned int)(x))
+#endif /* __POPCNT__ */

Selection of __bitcountl() should be based on sizeof long. Selection of __bitcount() should be based on sizeof int. Maybe it makes sense to add a test for this to the RTEMS testsuite and do a check of the pre-processor output on the arm-rtems4.12, sparc64-rtems4.12 and m32c-rtems4.12 targets.

--
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber@embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.


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