linux/include/linux/atomic.h
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   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 */
  15static 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
  44static 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
  64static 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
  77static 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
  97static 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
 115static 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 */
 132
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