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

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