From 3b8db5e93c4c02efbc313e17b2e796b0914a01fb Mon Sep 17 00:00:00 2001
From: Anton Tyurin <noxiouz@yandex.ru>
Date: Thu, 15 Dec 2016 20:56:52 +0100
Subject: [PATCH] Implement Add/Sub for Float64 (#17)

Signed-off-by: Anton Tiurin <noxiouz@yandex.ru>
---
 atomic.go      | 16 ++++++++++++++++
 atomic_test.go |  2 ++
 stress_test.go |  2 ++
 3 files changed, 20 insertions(+)

diff --git a/atomic.go b/atomic.go
index 4e21010..cd4aaa2 100644
--- a/atomic.go
+++ b/atomic.go
@@ -278,6 +278,22 @@ func (f *Float64) Store(s float64) {
 	atomic.StoreUint64(&f.v, math.Float64bits(s))
 }
 
+// Add atomically adds to the wrapped float64 and returns the new value.
+func (f *Float64) Add(s float64) float64 {
+	for {
+		old := f.Load()
+		new := old + s
+		if f.CAS(old, new) {
+			return new
+		}
+	}
+}
+
+// Sub atomically subtracts from the wrapped float64 and returns the new value.
+func (f *Float64) Sub(s float64) float64 {
+	return f.Add(-s)
+}
+
 // CAS is an atomic compare-and-swap.
 func (f *Float64) CAS(old, new float64) bool {
 	return atomic.CompareAndSwapUint64(&f.v, math.Float64bits(old), math.Float64bits(new))
diff --git a/atomic_test.go b/atomic_test.go
index 5fef44a..c21b831 100644
--- a/atomic_test.go
+++ b/atomic_test.go
@@ -128,4 +128,6 @@ func TestFloat64(t *testing.T) {
 
 	atom.Store(42.0)
 	require.Equal(t, float64(42.0), atom.Load(), "Store didn't set the correct value.")
+	require.Equal(t, float64(42.5), atom.Add(0.5), "Add didn't work.")
+	require.Equal(t, float64(42.0), atom.Sub(0.5), "Sub didn't work.")
 }
diff --git a/stress_test.go b/stress_test.go
index a030a4a..4cf1e16 100644
--- a/stress_test.go
+++ b/stress_test.go
@@ -110,6 +110,8 @@ func TestStressFloat64(t *testing.T) {
 	runStress(func() {
 		atom.Load()
 		atom.CAS(1.0, 0.1)
+		atom.Add(1.1)
+		atom.Sub(0.2)
 		atom.Store(1.0)
 	})
 }