cregit-Linux how code gets into the kernel

Release 4.7 include/asm-generic/word-at-a-time.h

#ifndef _ASM_WORD_AT_A_TIME_H

#define _ASM_WORD_AT_A_TIME_H

#include <linux/kernel.h>
#include <asm/byteorder.h>

#ifdef __BIG_ENDIAN


struct word_at_a_time {
	

const unsigned long high_bits, low_bits;
};


#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0xfe) + 1, REPEAT_BYTE(0x7f) }

/* Bit set in the bytes that have a zero */

static inline long prep_zero_mask(unsigned long val, unsigned long rhs, const struct word_at_a_time *c) { unsigned long mask = (val & c->low_bits) + c->low_bits; return ~(mask | rhs); }

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#define create_zero_mask(mask) (mask)
static inline long find_zero(unsigned long mask) { long byte = 0; #ifdef CONFIG_64BIT if (mask >> 32) mask >>= 32; else byte = 4; #endif if (mask >> 16) mask >>= 16; else byte += 2; return (mask >> 8) ? byte : byte + 1; }

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static inline bool has_zero(unsigned long val, unsigned long *data, const struct word_at_a_time *c) { unsigned long rhs = val | c->low_bits; *data = rhs; return (val + c->high_bits) & ~rhs; }

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#ifndef zero_bytemask #define zero_bytemask(mask) (~1ul << __fls(mask)) #endif #else /* * 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; }; #define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x01), REPEAT_BYTE(0x80) } #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) { return mask*0x0001020304050608ul >> 56; }

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#else /* 32-bit case */ /* Carl Chatfield / Jan Achrenius G+ version for 32-bit */
static inline long count_masked_bytes(long mask) { /* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */ long a = (0x0ff0001+mask) >> 23; /* Fix the 1 for 00 case */ return a & mask; }

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#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) { unsigned long mask = ((a - c->one_bits) & ~a) & c->high_bits; *bits = mask; return mask; }

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static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits, const struct word_at_a_time *c) { return bits; }

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static inline unsigned long create_zero_mask(unsigned long bits) { bits = (bits - 1) & ~bits; return bits >> 7; }

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/* 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); }

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#endif /* __BIG_ENDIAN */ #endif /* _ASM_WORD_AT_A_TIME_H */

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