add: arithmetic utilities

Author: changkun

Makefile

@@ -0,0 +1,13 @@
+COUNT := $(if $(COUNT),$(COUNT),1)
+
+all:
+	@echo "Usage:"
+	@echo "  - make tests: run all tests with race detection"
+	@echo "  - make bench count=<number>: run all benches with given count"
+
+tests:
+	go test -race -cover -coverprofile=cover.test -v .
+	go tool cover -html=cover.test -o cover.html
+
+bench:
+	go test -bench=. -benchmem -count=$(COUNT)

arithmetic.go

@@ -0,0 +1,20 @@
+package lockfree
+
+import (
+	"math"
+	"sync/atomic"
+	"unsafe"
+)
+
+// AddFloat64 add delta to given address atomically
+func AddFloat64(addr *float64, delta float64) (new float64) {
+	var old float64
+	for {
+		old = math.Float64frombits(atomic.LoadUint64((*uint64)(unsafe.Pointer(addr))))
+		if atomic.CompareAndSwapUint64((*uint64)(unsafe.Pointer(addr)),
+			math.Float64bits(old), math.Float64bits(old+delta)) {
+			break
+		}
+	}
+	return
+}

arithmetic_test.go

@@ -0,0 +1,31 @@
+package lockfree_test
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/changkun/lockfree"
+)
+
+func TestAddFloat64(t *testing.T) {
+	vs := []float64{}
+	for i := 1; i <= 10; i++ {
+		vs = append(vs, float64(i))
+	}
+
+	var sum float64
+	wg := sync.WaitGroup{}
+	wg.Add(10)
+	for _, v := range vs {
+		lv := v
+		go func() {
+			lockfree.AddFloat64(&sum, lv)
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+
+	if sum != float64(55) {
+		t.Fatalf("AddFloat64 wrong, expected 55, got %v", sum)
+	}
+}