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 struct 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  */
  27 static 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 */
  35 static 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 */
  46 static 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
  53 static 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
  58 static 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
  67 static 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  */
  79 static 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 */