const runtime.timeHistSubBucketBits

4 uses

	runtime (current package)
		histogram.go#L54: 	timeHistSubBucketBits   = 4
		histogram.go#L55: 	timeHistNumSubBuckets   = 1 << timeHistSubBucketBits
		histogram.go#L101: 		superBucket = uint(sys.Len64(uint64(duration))) - timeHistSubBucketBits
		histogram.go#L155: 			bucketNanos := uint64(1) << (i + timeHistSubBucketBits)