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powerpc: word-at-a-time optimization for 64-bit Little Endian

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This is an optimization for the PowerPC in 64-bit
little-endian. Bit counting is used in find_zero(), instead
of the multiply and shift.

It is modelled after Alan Modra's PowerPC LE strlen patch
http://sourceware.org/ml/libc-alpha/2013-08/msg00097.html.

Signed-off-by: Philippe Bergheaud <felix@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Philippe Bergheaud 2013-09-26 08:30:09 +02:00 committed by Benjamin Herrenschmidt
parent 9c662cad2f
commit d0cebfa650
1 changed files with 32 additions and 25 deletions
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57
arch/powerpc/include/asm/word-at-a-time.h
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@ -42,13 +42,6 @@ static inline bool has_zero(unsigned long val, unsigned long *data, const struct
#else
/*
* 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.
*/
struct word_at_a_time {
const unsigned long one_bits, high_bits;
};
@ -57,19 +50,32 @@ struct word_at_a_time {
#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)
/* Alan Modra's little-endian strlen tail for 64-bit */
#define create_zero_mask(mask) (mask)
static inline unsigned long find_zero(unsigned long mask)
{
return mask*0x0001020304050608ul >> 56;
unsigned long leading_zero_bits;
long trailing_zero_bit_mask;
asm ("addi %1,%2,-1\n\t"
"andc %1,%1,%2\n\t"
"popcntd %0,%1"
: "=r" (leading_zero_bits), "=&r" (trailing_zero_bit_mask)
: "r" (mask));
return leading_zero_bits >> 3;
}
#else /* 32-bit case */
/*
* 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.
*/
/* Carl Chatfield / Jan Achrenius G+ version for 32-bit */
static inline long count_masked_bytes(long mask)
{
@ -79,6 +85,17 @@ static inline long count_masked_bytes(long mask)
return a & mask;
}
static inline unsigned long create_zero_mask(unsigned long bits)
{
bits = (bits - 1) & ~bits;
return bits >> 7;
}
static inline unsigned long find_zero(unsigned long mask)
{
return count_masked_bytes(mask);
}
#endif
/* Return nonzero if it has a zero */
@ -94,19 +111,9 @@ static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits,
return bits;
}
static inline unsigned long create_zero_mask(unsigned long bits)
{
bits = (bits - 1) & ~bits;
return bits >> 7;
}
/* The mask we created is directly usable as a bytemask */
#define zero_bytemask(mask) (mask)
static inline unsigned long find_zero(unsigned long mask)
{
return count_masked_bytes(mask);
}
#endif
#endif /* _ASM_WORD_AT_A_TIME_H */