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

INCLUDED FROM

DEFINITIONS

1. count_masked_bytes
2. count_masked_bytes
3. has_zero
4. prep_zero_mask
5. create_zero_mask
6. find_zero
7. load_unaligned_zeropad

   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  */
  14 struct 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  */
  28 static 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 */
  36 static 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 */
  47 static 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 
  54 static 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 
  59 static 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 
  68 static 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  */
  80 static 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 */