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powerpc: ppc64le optimised word at a time

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Use cmpb which compares each byte in two 64 bit values and
for each matching byte places 0xff in the target and 0x00
otherwise.

A simple hash_name microbenchmark:

http://ozlabs.org/~anton/junkcode/hash_name_bench.c

shows this version to be 10-20% faster than running the x86
version on POWER8, depending on the length.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Anton Blanchard 2014-09-19 09:40:20 +10:00 committed by Michael Ellerman
parent fe2a1bb1db
commit 8989aa4ada
1 changed files with 56 additions and 23 deletions
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79
arch/powerpc/include/asm/word-at-a-time.h
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@ -42,32 +42,65 @@ static inline bool has_zero(unsigned long val, unsigned long *data, const struct
#else
#ifdef CONFIG_64BIT
/* unused */
struct word_at_a_time {
};
#define WORD_AT_A_TIME_CONSTANTS { }
/* This will give us 0xff for a NULL char and 0x00 elsewhere */
static inline unsigned long has_zero(unsigned long a, unsigned long *bits, const struct word_at_a_time *c)
{
unsigned long ret;
unsigned long zero = 0;
asm("cmpb %0,%1,%2" : "=r" (ret) : "r" (a), "r" (zero));
*bits = ret;
return ret;
}
static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits, const struct word_at_a_time *c)
{
return bits;
}
/* Alan Modra's little-endian strlen tail for 64-bit */
static inline unsigned long create_zero_mask(unsigned long bits)
{
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" (bits));
return leading_zero_bits;
}
static inline unsigned long find_zero(unsigned long mask)
{
return mask >> 3;
}
/* This assumes that we never ask for an all 1s bitmask */
static inline unsigned long zero_bytemask(unsigned long mask)
{
return (1UL << mask) - 1;
}
#else /* 32-bit case */
struct word_at_a_time {
const unsigned long one_bits, high_bits;
};
#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x01), REPEAT_BYTE(0x80) }
#ifdef CONFIG_64BIT
/* 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)
{
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
@ -96,8 +129,6 @@ static inline unsigned long find_zero(unsigned long mask)
return count_masked_bytes(mask);
}
#endif
/* Return nonzero if it has a zero */
static inline unsigned long has_zero(unsigned long a, unsigned long *bits, const struct word_at_a_time *c)
{
@ -114,7 +145,9 @@ static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits,
/* The mask we created is directly usable as a bytemask */
#define zero_bytemask(mask) (mask)
#endif
#endif /* CONFIG_64BIT */
#endif /* __BIG_ENDIAN__ */
/*
* We use load_unaligned_zero() in a selftest, which builds a userspace