From d0cebfa650a084f041131207d81f9b311babd5ef Mon Sep 17 00:00:00 2001 From: Philippe Bergheaud Date: Thu, 26 Sep 2013 08:30:09 +0200 Subject: [PATCH] powerpc: word-at-a-time optimization for 64-bit Little Endian 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 Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/include/asm/word-at-a-time.h | 57 +++++++++++++---------- 1 file changed, 32 insertions(+), 25 deletions(-) diff --git a/arch/powerpc/include/asm/word-at-a-time.h b/arch/powerpc/include/asm/word-at-a-time.h index 213a5f2b0717..9a5c928bb3c6 100644 --- a/arch/powerpc/include/asm/word-at-a-time.h +++ b/arch/powerpc/include/asm/word-at-a-time.h @@ -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 */ -- 2.20.1