2 files changed, 29 insertions, 0 deletions
diff --git a/src/testing/benchmark.go b/src/testing/benchmark.go
index 5591cd4e4d..0271308346 100644
--- a/src/testing/benchmark.go
+++ b/src/testing/benchmark.go
@@ -113,6 +113,8 @@ type B struct {
 	netBytes  uint64
 	// Extra metrics collected by ReportMetric.
 	extra map[string]float64
+	// Remaining iterations of Loop() to be executed in benchFunc.
+	loopN int
 }
 
 // StartTimer starts timing a test. This function is called automatically
@@ -187,6 +189,7 @@ func (b *B) runN(n int) {
 	runtime.GC()
 	b.resetRaces()
 	b.N = n
+	b.loopN = n
 	b.parallelism = 1
 	b.ResetTimer()
 	b.StartTimer()
@@ -349,6 +352,16 @@ func (b *B) ReportMetric(n float64, unit string) {
 	b.extra[unit] = n
 }
 
+// Loop returns true until b.N calls has been made to it.
+//
+// A benchmark should either use Loop or contain an explicit loop from 0 to b.N, but not both.
+// After the benchmark finishes, b.N will contain the total number of calls to op, so the benchmark
+// may use b.N to compute other average metrics.
+func (b *B) Loop() bool {
+	b.loopN--
+	return b.loopN >= 0
+}
+
 // BenchmarkResult contains the results of a benchmark run.
 type BenchmarkResult struct {
 	N         int           // The number of iterations.
diff --git a/src/testing/benchmark_test.go b/src/testing/benchmark_test.go
index 66f555d1f1..b5ad213fb3 100644
--- a/src/testing/benchmark_test.go
+++ b/src/testing/benchmark_test.go
@@ -127,6 +127,22 @@ func TestRunParallelSkipNow(t *testing.T) {
 	})
 }
 
+func TestLoopEqualsRangeOverBN(t *testing.T) {
+	// Verify that b.N and the b.Loop() iteration count match.
+	var nIterated, nInfered int
+	testing.Benchmark(func(b *testing.B) {
+		i := 0
+		for b.Loop() {
+			i++
+		}
+		nIterated = i
+		nInfered = b.N
+	})
+	if nIterated != nInfered {
+		t.Fatalf("Iteration of the two different benchmark loop flavor differs, got %d iterations want %d", nIterated, nInfered)
+	}
+}
+
 func ExampleB_RunParallel() {
 	// Parallel benchmark for text/template.Template.Execute on a single object.
 	testing.Benchmark(func(b *testing.B) {