Commit 821376bf authored by David Mosberger-Tang's avatar David Mosberger-Tang Committed by Tony Luck
Browse files

[IA64] fix fls() 



The ia64-version of fls() never worked as intended (the bitnumbering
was off by 1 and fls(0) was undefined).  This patch fixes the problem
by using a popcnt-based fls(), which on McKinley-derived cores is
slightly faster than both ia64_fls() and generic_fls().  The resulting
code, however, is bigger (7-8 bundles instead of about 3 bundles).
Also switch ia64_popcnt() to __builtin_popcountl() for GCC v3.4 or
newer since the compiler can predicate that and schedule it better.

Thanks to Simon Derr and Matt Mackall for tracking down this bug.

Signed-off-by: default avatarDavid Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
parent d8470b7c

include/asm-ia64/bitops.h

+17 −4
Original line number Diff line number Diff line
@@ -314,8 +314,8 @@ __ffs (unsigned long x) 
#ifdef __KERNEL__



/*

 * find_last_zero_bit - find the last zero bit in a 64 bit quantity

 * @x: The value to search

 * Return bit number of last (most-significant) bit set.  Undefined

 * for x==0.  Bits are numbered from 0..63 (e.g., ia64_fls(9) == 3).

 */

static inline unsigned long

ia64_fls (unsigned long x)
@@ -327,10 +327,23 @@ ia64_fls (unsigned long x) 
	return exp - 0xffff;

}



/*

 * Find the last (most significant) bit set.  Returns 0 for x==0 and

 * bits are numbered from 1..32 (e.g., fls(9) == 4).

 */

static inline int

fls (int x)

fls (int t)

{

	return ia64_fls((unsigned int) x);

	unsigned long x = t & 0xffffffffu;



	if (!x)

		return 0;

	x |= x >> 1;

	x |= x >> 2;

	x |= x >> 4;

	x |= x >> 8;

	x |= x >> 16;

	return ia64_popcnt(x);

}



/*

include/asm-ia64/gcc_intrin.h

+7 −3
Original line number Diff line number Diff line
@@ -133,6 +133,9 @@ register unsigned long ia64_r13 asm ("r13") __attribute_used__; 
	ia64_intri_res;								\

})



#if __GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)

# define ia64_popcnt(x)		__builtin_popcountl(x)

#else

# define ia64_popcnt(x)						\

  ({								\

	__u64 ia64_intri_res;					\
@@ -140,6 +143,7 @@ register unsigned long ia64_r13 asm ("r13") __attribute_used__; 
								\

	ia64_intri_res;						\

  })

#endif



#define ia64_getf_exp(x)					\

({								\

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