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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>
120 lines
2.8 KiB
C
120 lines
2.8 KiB
C
#ifndef _ASM_WORD_AT_A_TIME_H
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#define _ASM_WORD_AT_A_TIME_H
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/*
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* Word-at-a-time interfaces for PowerPC.
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*/
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#include <linux/kernel.h>
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#include <asm/asm-compat.h>
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#ifdef __BIG_ENDIAN__
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struct word_at_a_time {
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const unsigned long high_bits, low_bits;
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};
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#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0xfe) + 1, REPEAT_BYTE(0x7f) }
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/* Bit set in the bytes that have a zero */
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static inline long prep_zero_mask(unsigned long val, unsigned long rhs, const struct word_at_a_time *c)
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{
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unsigned long mask = (val & c->low_bits) + c->low_bits;
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return ~(mask | rhs);
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}
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#define create_zero_mask(mask) (mask)
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static inline long find_zero(unsigned long mask)
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{
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long leading_zero_bits;
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asm (PPC_CNTLZL "%0,%1" : "=r" (leading_zero_bits) : "r" (mask));
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return leading_zero_bits >> 3;
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}
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static inline bool has_zero(unsigned long val, unsigned long *data, const struct word_at_a_time *c)
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{
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unsigned long rhs = val | c->low_bits;
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*data = rhs;
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return (val + c->high_bits) & ~rhs;
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}
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#else
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struct word_at_a_time {
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const unsigned long one_bits, high_bits;
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};
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#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x01), REPEAT_BYTE(0x80) }
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#ifdef CONFIG_64BIT
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/* Alan Modra's little-endian strlen tail for 64-bit */
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#define create_zero_mask(mask) (mask)
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static inline unsigned long find_zero(unsigned long mask)
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{
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unsigned long leading_zero_bits;
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long trailing_zero_bit_mask;
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asm ("addi %1,%2,-1\n\t"
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"andc %1,%1,%2\n\t"
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"popcntd %0,%1"
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: "=r" (leading_zero_bits), "=&r" (trailing_zero_bit_mask)
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: "r" (mask));
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return leading_zero_bits >> 3;
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}
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#else /* 32-bit case */
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/*
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* This is largely generic for little-endian machines, but the
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* optimal byte mask counting is probably going to be something
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* that is architecture-specific. If you have a reliably fast
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* bit count instruction, that might be better than the multiply
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* and shift, for example.
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*/
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/* Carl Chatfield / Jan Achrenius G+ version for 32-bit */
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static inline long count_masked_bytes(long mask)
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{
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/* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */
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long a = (0x0ff0001+mask) >> 23;
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/* Fix the 1 for 00 case */
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return a & mask;
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}
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static inline unsigned long create_zero_mask(unsigned long bits)
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{
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bits = (bits - 1) & ~bits;
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return bits >> 7;
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}
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static inline unsigned long find_zero(unsigned long mask)
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{
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return count_masked_bytes(mask);
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}
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#endif
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/* Return nonzero if it has a zero */
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static inline unsigned long has_zero(unsigned long a, unsigned long *bits, const struct word_at_a_time *c)
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{
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unsigned long mask = ((a - c->one_bits) & ~a) & c->high_bits;
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*bits = mask;
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return mask;
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}
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static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits, const struct word_at_a_time *c)
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{
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return bits;
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}
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/* The mask we created is directly usable as a bytemask */
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#define zero_bytemask(mask) (mask)
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#endif
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#endif /* _ASM_WORD_AT_A_TIME_H */
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