1 files changed, 27 insertions, 1 deletions
diff --git a/libgo/go/testing/cover.go b/libgo/go/testing/cover.go
index dd29364d87..a4ce37f7c2 100644
--- a/libgo/go/testing/cover.go
+++ b/libgo/go/testing/cover.go
@@ -9,6 +9,7 @@ package testing
 import (
 	"fmt"
 	"os"
+	"sync/atomic"
 )
 
 // CoverBlock records the coverage data for a single basic block.
@@ -34,6 +35,29 @@ type Cover struct {
 	CoveredPackages string
 }
 
+// Coverage reports the current code coverage as a fraction in the range [0, 1].
+// If coverage is not enabled, Coverage returns 0.
+//
+// When running a large set of sequential test cases, checking Coverage after each one
+// can be useful for identifying which test cases exercise new code paths.
+// It is not a replacement for the reports generated by 'go test -cover' and
+// 'go tool cover'.
+func Coverage() float64 {
+	var n, d int64
+	for _, counters := range cover.Counters {
+		for i := range counters {
+			if atomic.LoadUint32(&counters[i]) > 0 {
+				n++
+			}
+			d++
+		}
+	}
+	if d == 0 {
+		return 0
+	}
+	return float64(n) / float64(d)
+}
+
 // RegisterCover records the coverage data accumulators for the tests.
 // NOTE: This function is internal to the testing infrastructure and may change.
 // It is not covered (yet) by the Go 1 compatibility guidelines.
@@ -61,11 +85,13 @@ func coverReport() {
 	}
 
 	var active, total int64
+	var count uint32
 	for name, counts := range cover.Counters {
 		blocks := cover.Blocks[name]
-		for i, count := range counts {
+		for i := range counts {
 			stmts := int64(blocks[i].Stmts)
 			total += stmts
+			count = atomic.LoadUint32(&counts[i]) // For -mode=atomic.
 			if count > 0 {
 				active += stmts
 			}