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word-at-a-time.h
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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 */