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Commit f68e556e authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Make the "word-at-a-time" helper functions more commonly usable 



I have a new optimized x86 "strncpy_from_user()" that will use these
same helper functions for all the same reasons the name lookup code uses
them.  This is preparation for that.

This moves them into an architecture-specific header file.  It's
architecture-specific for two reasons:

 - some of the functions are likely to want architecture-specific
   implementations.  Even if the current code happens to be "generic" in
   the sense that it should work on any little-endian machine, it's
   likely that the "multiply by a big constant and shift" implementation
   is less than optimal for an architecture that has a guaranteed fast
   bit count instruction, for example.

 - I expect that if architectures like sparc want to start playing
   around with this, we'll need to abstract out a few more details (in
   particular the actual unaligned accesses).  So we're likely to have
   more architecture-specific stuff if non-x86 architectures start using
   this.

   (and if it turns out that non-x86 architectures don't start using
   this, then having it in an architecture-specific header is still the
   right thing to do, of course)

Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 23f347ef

arch/x86/include/asm/word-at-a-time.h

0 → 100644
+46 −0
Original line number Diff line number Diff line 
#ifndef _ASM_WORD_AT_A_TIME_H

#define _ASM_WORD_AT_A_TIME_H



/*

 * This is largely generic for little-endian machines, but the

 * optimal byte mask counting is probably going to be something

 * that is architecture-specific. If you have a reliably fast

 * bit count instruction, that might be better than the multiply

 * and shift, for example.

 */



#ifdef CONFIG_64BIT



/*

 * Jan Achrenius on G+: microoptimized version of

 * the simpler "(mask & ONEBYTES) * ONEBYTES >> 56"

 * that works for the bytemasks without having to

 * mask them first.

 */

static inline long count_masked_bytes(unsigned long mask)

{

	return mask*0x0001020304050608ul >> 56;

}



#else	/* 32-bit case */



/* Carl Chatfield / Jan Achrenius G+ version for 32-bit */

static inline long count_masked_bytes(long mask)

{

	/* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */

	long a = (0x0ff0001+mask) >> 23;

	/* Fix the 1 for 00 case */

	return a & mask;

}



#endif



#define REPEAT_BYTE(x)	((~0ul / 0xff) * (x))



/* Return the high bit set in the first byte that is a zero */

static inline unsigned long has_zero(unsigned long a)

{

	return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80);

}



#endif /* _ASM_WORD_AT_A_TIME_H */

fs/namei.c

+3 −32
Original line number Diff line number Diff line
@@ -1407,18 +1407,9 @@ static inline int can_lookup(struct inode *inode) 
 */

#ifdef CONFIG_DCACHE_WORD_ACCESS



#ifdef CONFIG_64BIT

#include <asm/word-at-a-time.h>



/*

 * Jan Achrenius on G+: microoptimized version of

 * the simpler "(mask & ONEBYTES) * ONEBYTES >> 56"

 * that works for the bytemasks without having to

 * mask them first.

 */

static inline long count_masked_bytes(unsigned long mask)

{

	return mask*0x0001020304050608ul >> 56;

}

#ifdef CONFIG_64BIT



static inline unsigned int fold_hash(unsigned long hash)

{
@@ -1428,15 +1419,6 @@ static inline unsigned int fold_hash(unsigned long hash) 


#else	/* 32-bit case */



/* Carl Chatfield / Jan Achrenius G+ version for 32-bit */

static inline long count_masked_bytes(long mask)

{

	/* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */

	long a = (0x0ff0001+mask) >> 23;

	/* Fix the 1 for 00 case */

	return a & mask;

}



#define fold_hash(x) (x)



#endif
@@ -1464,17 +1446,6 @@ done: 
}

EXPORT_SYMBOL(full_name_hash);



#define REPEAT_BYTE(x)	((~0ul / 0xff) * (x))

#define ONEBYTES	REPEAT_BYTE(0x01)

#define SLASHBYTES	REPEAT_BYTE('/')

#define HIGHBITS	REPEAT_BYTE(0x80)



/* Return the high bit set in the first byte that is a zero */

static inline unsigned long has_zero(unsigned long a)

{

	return ((a - ONEBYTES) & ~a) & HIGHBITS;

}



/*

 * Calculate the length and hash of the path component, and

 * return the length of the component;
@@ -1490,7 +1461,7 @@ static inline unsigned long hash_name(const char *name, unsigned int *hashp) 
		len += sizeof(unsigned long);

		a = *(unsigned long *)(name+len);

		/* Do we have any NUL or '/' bytes in this word? */

		mask = has_zero(a) | has_zero(a ^ SLASHBYTES);

		mask = has_zero(a) | has_zero(a ^ REPEAT_BYTE('/'));

	} while (!mask);



	/* The mask *below* the first high bit set */