testing: scale benchmark precision to 0.01ns if needed

R=dvyukov, r
CC=golang-dev
https://golang.org/cl/4657053

diff --git a/src/pkg/testing/benchmark.go b/src/pkg/testing/benchmark.go
index 0ee879709d8af584a55e2fbb3c44f075d358ba40..4d5ff6c77688a91475b7456c316fe46b89adaf81 100644 (file)
--- a/src/pkg/testing/benchmark.go
+++ b/src/pkg/testing/benchmark.go
@@ -174,7 +174,18 @@ func (r BenchmarkResult) String() string {
        if mbs != 0 {
                mb = fmt.Sprintf("\t%7.2f MB/s", mbs)
        }
-       return fmt.Sprintf("%8d\t%10d ns/op%s", r.N, r.NsPerOp(), mb)
+       nsop := r.NsPerOp()
+       ns := fmt.Sprintf("%10d ns/op", nsop)
+       if r.N > 0 && nsop < 100 {
+               // The format specifiers here make sure that
+               // the ones digits line up for all three possible formats.
+               if nsop < 10 {
+                       ns = fmt.Sprintf("%13.2f ns/op", float64(r.Ns)/float64(r.N))
+               } else {
+                       ns = fmt.Sprintf("%12.1f ns/op", float64(r.Ns)/float64(r.N))
+               }
+       }
+       return fmt.Sprintf("%8d\t%s%s", r.N, ns, mb)
 }
 
 // An internal function but exported because it is cross-package; part of the implementation