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Whilst architectures may be able to do better than this (which they can, by simply defining their own macro), this is a generic stab at a zero_bytemask implementation for the asm-generic, big-endian word-at-a-time implementation. On arm64, a clz instruction is used to implement the fls efficiently. Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
61 lines
1.4 KiB
C
61 lines
1.4 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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* This says "generic", but it's actually big-endian only.
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* Little-endian can use more efficient versions of these
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* interfaces, see for example
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* arch/x86/include/asm/word-at-a-time.h
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* for those.
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*/
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#include <linux/kernel.h>
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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 byte = 0;
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#ifdef CONFIG_64BIT
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if (mask >> 32)
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mask >>= 32;
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else
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byte = 4;
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#endif
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if (mask >> 16)
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mask >>= 16;
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else
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byte += 2;
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return (mask >> 8) ? byte : byte + 1;
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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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#ifndef zero_bytemask
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#ifdef CONFIG_64BIT
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#define zero_bytemask(mask) (~0ul << fls64(mask))
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#else
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#define zero_bytemask(mask) (~0ul << fls(mask))
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#endif /* CONFIG_64BIT */
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#endif /* zero_bytemask */
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#endif /* _ASM_WORD_AT_A_TIME_H */
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