1 files changed, 36 insertions, 0 deletions
diff --git a/libgo/go/runtime/fastlog2_test.go b/libgo/go/runtime/fastlog2_test.go
new file mode 100644
index 00000000000..8f92dc66942
--- /dev/null
+++ b/libgo/go/runtime/fastlog2_test.go
@@ -0,0 +1,36 @@
+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+package runtime_test
+
+import (
+	"math"
+	"runtime"
+	"testing"
+)
+
+func TestFastLog2(t *testing.T) {
+	// Compute the euclidean distance between math.Log2 and the FastLog2
+	// implementation over the range of interest for heap sampling.
+	const randomBitCount = 26
+	var e float64
+
+	inc := 1
+	if testing.Short() {
+		// Check 1K total values, down from 64M.
+		inc = 1 << 16
+	}
+	for i := 1; i < 1<<randomBitCount; i += inc {
+		l, fl := math.Log2(float64(i)), runtime.Fastlog2(float64(i))
+		d := l - fl
+		e += d * d
+	}
+	e = math.Sqrt(e)
+
+	if e > 1.0 {
+		t.Fatalf("imprecision on fastlog2 implementation, want <=1.0, got %f", e)
+	}
+}