adding rough inc / dec functions

Author: leios

src/atomics.jl

@@ -49,19 +49,26 @@ for (name, op) in ops
     end
 end
 
-# TODO: Not sure what this one is...
 function atomic_cas!(ptr::Ptr{T}, old::T, new::T) where T
     Core.Intrinsics.atomic_pointerreplace(ptr::Ptr{T}, old, new, :release_acquire, :monotonic)
 end
 
-# TODO: Not sure what this one is...
+# Implementation of: (((old == 0) | (old > b)) ? b : (old-1)), returns old
 function atomic_dec!(ptr::Ptr{T}, b::T) where T
-    Core.Intrinsics.atomic_pointermodify(ptr, -, 1, :monotonic)
+    if (unsafe_load(ptr) == 0 | unsafe_load(ptr) > b)
+        Core.Intrinsics.atomic_pointerswap(ptr, b, :monotonic)
+    else
+        Core.Intrinsics.atomic_pointermodify(ptr, -, 1, :monotonic)
+    end
 end
 
-# TODO: Not sure what this one is...
+# implementation of: ((old >= b) ? 0 : (old+1)), returns old
 function atomic_inc!(ptr::Ptr{T}, b::T) where T
-    Core.Intrinsics.atomic_pointermodify(ptr, +, 1, :monotonic)
+    if unsafe_load(ptr) >= b
+        Core.Intrinsics.atomic_pointerswap(ptr, 0, :monotonic)
+    else
+        Core.Intrinsics.atomic_pointermodify(ptr, +, 1, :monotonic)
+    end
 end
 
 function atomic_xchg!(ptr::Ptr{T}, b::T) where T