include/linux/atomic.h

   1 /* Atomic operations usable in machine independent code */
   2 #ifndef _LINUX_ATOMIC_H
   3 #define _LINUX_ATOMIC_H
   4 #include <asm/atomic.h>
   5
   6 /**
   7  * atomic_add_unless - add unless the number is already a given value
   8  * @v: pointer of type atomic_t
   9  * @a: the amount to add to v...
  10  * @u: ...unless v is equal to u.
  11  *
  12  * Atomically adds @a to @v, so long as @v was not already @u.
  13  * Returns non-zero if @v was not @u, and zero otherwise.
  14  */
  15 static inline int atomic_add_unless(atomic_t *v, int a, int u)
  16 {
  17         return __atomic_add_unless(v, a, u) != u;
  18 }
  19
  20 /**
  21  * atomic_inc_not_zero - increment unless the number is zero
  22  * @v: pointer of type atomic_t
  23  *
  24  * Atomically increments @v by 1, so long as @v is non-zero.
  25  * Returns non-zero if @v was non-zero, and zero otherwise.
  26  */
  27 #ifndef atomic_inc_not_zero
  28 #define atomic_inc_not_zero(v)          atomic_add_unless((v), 1, 0)
  29 #endif
  30
  31 /**
  32  * atomic_inc_not_zero_hint - increment if not null
  33  * @v: pointer of type atomic_t
  34  * @hint: probable value of the atomic before the increment
  35  *
  36  * This version of atomic_inc_not_zero() gives a hint of probable
  37  * value of the atomic. This helps processor to not read the memory
  38  * before doing the atomic read/modify/write cycle, lowering
  39  * number of bus transactions on some arches.
  40  *
  41  * Returns: 0 if increment was not done, 1 otherwise.
  42  */
  43 #ifndef atomic_inc_not_zero_hint
  44 static inline int atomic_inc_not_zero_hint(atomic_t *v, int hint)
  45 {
  46         int val, c = hint;
  47
  48         /* sanity test, should be removed by compiler if hint is a constant */
  49         if (!hint)
  50                 return atomic_inc_not_zero(v);
  51
  52         do {
  53                 val = atomic_cmpxchg(v, c, c + 1);
  54                 if (val == c)
  55                         return 1;
  56                 c = val;
  57         } while (c);
  58
  59         return 0;
  60 }
  61 #endif
  62
  63 #ifndef atomic_inc_unless_negative
  64 static inline int atomic_inc_unless_negative(atomic_t *p)
  65 {
  66         int v, v1;
  67         for (v = 0; v >= 0; v = v1) {
  68                 v1 = atomic_cmpxchg(p, v, v + 1);
  69                 if (likely(v1 == v))
  70                         return 1;
  71         }
  72         return 0;
  73 }
  74 #endif
  75
  76 #ifndef atomic_dec_unless_positive
  77 static inline int atomic_dec_unless_positive(atomic_t *p)
  78 {
  79         int v, v1;
  80         for (v = 0; v <= 0; v = v1) {
  81                 v1 = atomic_cmpxchg(p, v, v - 1);
  82                 if (likely(v1 == v))
  83                         return 1;
  84         }
  85         return 0;
  86 }
  87 #endif
  88
  89 /*
  90  * atomic_dec_if_positive - decrement by 1 if old value positive
  91  * @v: pointer of type atomic_t
  92  *
  93  * The function returns the old value of *v minus 1, even if
  94  * the atomic variable, v, was not decremented.
  95  */
  96 #ifndef atomic_dec_if_positive
  97 static inline int atomic_dec_if_positive(atomic_t *v)
  98 {
  99         int c, old, dec;
 100         c = atomic_read(v);
 101         for (;;) {
 102                 dec = c - 1;
 103                 if (unlikely(dec < 0))
 104                         break;
 105                 old = atomic_cmpxchg((v), c, dec);
 106                 if (likely(old == c))
 107                         break;
 108                 c = old;
 109         }
 110         return dec;
 111 }
 112 #endif
 113
 114 #ifndef CONFIG_ARCH_HAS_ATOMIC_OR
 115 static inline void atomic_or(int i, atomic_t *v)
 116 {
 117         int old;
 118         int new;
 119
 120         do {
 121                 old = atomic_read(v);
 122                 new = old | i;
 123         } while (atomic_cmpxchg(v, old, new) != old);
 124 }
 125 #endif /* #ifndef CONFIG_ARCH_HAS_ATOMIC_OR */
 126
 127 #include <asm-generic/atomic-long.h>
 128 #ifdef CONFIG_GENERIC_ATOMIC64
 129 #include <asm-generic/atomic64.h>
 130 #endif
 131 #endif /* _LINUX_ATOMIC_H */