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  */
  13
  14 #ifdef CONFIG_64BIT
  15
  16 /*
  17  * Jan Achrenius on G+: microoptimized version of
  18  * the simpler "(mask & ONEBYTES) * ONEBYTES >> 56"
  19  * that works for the bytemasks without having to
  20  * mask them first.
  21  */
  22 static inline long count_masked_bytes(unsigned long mask)
  23 {
  24         return mask*0x0001020304050608ul >> 56;
  25 }
  26
  27 #else   /* 32-bit case */
  28
  29 /* Carl Chatfield / Jan Achrenius G+ version for 32-bit */
  30 static inline long count_masked_bytes(long mask)
  31 {
  32         /* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */
  33         long a = (0x0ff0001+mask) >> 23;
  34         /* Fix the 1 for 00 case */
  35         return a & mask;
  36 }
  37
  38 #endif
  39
  40 /* Return the high bit set in the first byte that is a zero */
  41 static inline unsigned long has_zero(unsigned long a)
  42 {
  43         return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80);
  44 }
  45
  46 /*
  47  * Load an unaligned word from kernel space.
  48  *
  49  * In the (very unlikely) case of the word being a page-crosser
  50  * and the next page not being mapped, take the exception and
  51  * return zeroes in the non-existing part.
  52  */
  53 static inline unsigned long load_unaligned_zeropad(const void *addr)
  54 {
  55         unsigned long ret, dummy;
  56
  57         asm(
  58                 "1:\tmov %2,%0\n"
  59                 "2:\n"
  60                 ".section .fixup,\"ax\"\n"
  61                 "3:\t"
  62                 "lea %2,%1\n\t"
  63                 "and %3,%1\n\t"
  64                 "mov (%1),%0\n\t"
  65                 "leal %2,%%ecx\n\t"
  66                 "andl %4,%%ecx\n\t"
  67                 "shll $3,%%ecx\n\t"
  68                 "shr %%cl,%0\n\t"
  69                 "jmp 2b\n"
  70                 ".previous\n"
  71                 _ASM_EXTABLE(1b, 3b)
  72                 :"=&r" (ret),"=&c" (dummy)
  73                 :"m" (*(unsigned long *)addr),
  74                  "i" (-sizeof(unsigned long)),
  75                  "i" (sizeof(unsigned long)-1));
  76         return ret;
  77 }
  78
  79 #endif /* _ASM_WORD_AT_A_TIME_H */