[PATCH 1/4] atomic: add atomic_add_unless()

[Lionel Landwerlin]

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
---
 xf86atomic.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/xf86atomic.h b/xf86atomic.h
index db2f619..bc482c9 100644
--- a/xf86atomic.h
+++ b/xf86atomic.h
@@ -96,4 +96,13 @@ typedef struct { uint_t atomic; } atomic_t;
 #error libdrm requires atomic operations, please define them for your CPU/compiler.
 #endif
 
+static inline int atomic_add_unless(atomic_t *v, int add, int unless)
+{
+	int c, old;
+	c = atomic_read(v);
+	while (c != unless && (old = atomic_cmpxchg(v, c, c + add)) != c)
+		c = old;
+	return c == unless;
+}
+
 #endif
-- 
2.0.1