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[PATCH v2 3/4] x86: use POPCNT for hweight<N>() when available
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 19 Jul 2023 11:44:36 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 19 Jul 2023 09:44:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
This is faster than using the software implementation, and the insn is
available on all half-way recent hardware. Use the respective compiler
builtins when available.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Jason Andryuk <jandryuk@xxxxxxxxx>
--- a/xen/arch/x86/include/asm/bitops.h
+++ b/xen/arch/x86/include/asm/bitops.h
@@ -475,9 +475,16 @@ static inline int fls(unsigned int x)
*
* The Hamming Weight of a number is the total number of bits set in it.
*/
+#ifdef __POPCNT__
+#define hweight64(x) __builtin_popcountll(x)
+#define hweight32(x) __builtin_popcount(x)
+#define hweight16(x) __builtin_popcount((uint16_t)(x))
+#define hweight8(x) __builtin_popcount((uint8_t)(x))
+#else
#define hweight64(x) generic_hweight64(x)
#define hweight32(x) generic_hweight32(x)
#define hweight16(x) generic_hweight16(x)
#define hweight8(x) generic_hweight8(x)
+#endif
#endif /* _X86_BITOPS_H */
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