[POWERPC] Optimize fls64() on 64-bit processors (9f264be6) · Commits · 戴 / test

64-bit powerpc processors can find the leftmost 1 bit in a 64-bit doubleword in one instruction, so use that rather than using the generic fls64(), which does two 32-bit fls() calls. Signed-off-by:

Paul Mackerras <paulus@samba.org>

include/asm-powerpc/bitops.h

+17 −0

Original line number	Diff line number	Diff line
		@@ -312,7 +312,24 @@ static __inline__ int fls(unsigned int x)
		asm ("cntlzw %0,%1" : "=r" (lz) : "r" (x));
		return 32 - lz;
		}

		/*
		* 64-bit can do this using one cntlzd (count leading zeroes doubleword)
		* instruction; for 32-bit we use the generic version, which does two
		* 32-bit fls calls.
		*/
		#ifdef __powerpc64__
		static __inline__ int fls64(__u64 x)
		{
		int lz;

		asm ("cntlzd %0,%1" : "=r" (lz) : "r" (x));
		return 64 - lz;
		}
		#else
		#include <asm-generic/bitops/fls64.h>
		#endif /* __powerpc64__ */

		#include <asm-generic/bitops/hweight.h>
		#include <asm-generic/bitops/find.h>

Admin message