LXR linux/arch/x86/include/asm/word-at-a-time.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef _ASM_WORD_AT_A_TIME_H
   3#define _ASM_WORD_AT_A_TIME_H
   4
   5#include <linux/kernel.h>
   6
   7/*
   8 * This is largely generic for little-endian machines, but the
   9 * optimal byte mask counting is probably going to be something
  10 * that is architecture-specific. If you have a reliably fast
  11 * bit count instruction, that might be better than the multiply
  12 * and shift, for example.
  13 */
  14struct word_at_a_time {
  15        const unsigned long one_bits, high_bits;
  16};
  17
  18#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x01), REPEAT_BYTE(0x80) }
  19
  20#ifdef CONFIG_64BIT
  21
  22/*
  23 * Jan Achrenius on G+: microoptimized version of
  24 * the simpler "(mask & ONEBYTES) * ONEBYTES >> 56"
  25 * that works for the bytemasks without having to
  26 * mask them first.
  27 */
  28static inline long count_masked_bytes(unsigned long mask)
  29{
  30        return mask*0x0001020304050608ul >> 56;
  31}
  32
  33#else   /* 32-bit case */
  34
  35/* Carl Chatfield / Jan Achrenius G+ version for 32-bit */
  36static inline long count_masked_bytes(long mask)
  37{
  38        /* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */
  39        long a = (0x0ff0001+mask) >> 23;
  40        /* Fix the 1 for 00 case */
  41        return a & mask;
  42}
  43
  44#endif
  45
  46/* Return nonzero if it has a zero */
  47static inline unsigned long has_zero(unsigned long a, unsigned long *bits, const struct word_at_a_time *c)
  48{
  49        unsigned long mask = ((a - c->one_bits) & ~a) & c->high_bits;
  50        *bits = mask;
  51        return mask;
  52}
  53
  54static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits, const struct word_at_a_time *c)
  55{
  56        return bits;
  57}
  58
  59static inline unsigned long create_zero_mask(unsigned long bits)
  60{
  61        bits = (bits - 1) & ~bits;
  62        return bits >> 7;
  63}
  64
  65/* The mask we created is directly usable as a bytemask */
  66#define zero_bytemask(mask) (mask)
  67
  68static inline unsigned long find_zero(unsigned long mask)
  69{
  70        return count_masked_bytes(mask);
  71}
  72
  73/*
  74 * Load an unaligned word from kernel space.
  75 *
  76 * In the (very unlikely) case of the word being a page-crosser
  77 * and the next page not being mapped, take the exception and
  78 * return zeroes in the non-existing part.
  79 */
  80static inline unsigned long load_unaligned_zeropad(const void *addr)
  81{
  82        unsigned long ret, dummy;
  83
  84        asm(
  85                "1:\tmov %2,%0\n"
  86                "2:\n"
  87                ".section .fixup,\"ax\"\n"
  88                "3:\t"
  89                "lea %2,%1\n\t"
  90                "and %3,%1\n\t"
  91                "mov (%1),%0\n\t"
  92                "leal %2,%%ecx\n\t"
  93                "andl %4,%%ecx\n\t"
  94                "shll $3,%%ecx\n\t"
  95                "shr %%cl,%0\n\t"
  96                "jmp 2b\n"
  97                ".previous\n"
  98                _ASM_EXTABLE(1b, 3b)
  99                :"=&r" (ret),"=&c" (dummy)
 100                :"m" (*(unsigned long *)addr),
 101                 "i" (-sizeof(unsigned long)),
 102                 "i" (sizeof(unsigned long)-1));
 103        return ret;
 104}
 105
 106#endif /* _ASM_WORD_AT_A_TIME_H */
 107