pkg/cover: add MergeDiff method

Will be used in the next patch.

2 files changed, 83 insertions, 0 deletions

diff --git a/pkg/cover/cover.go b/pkg/cover/cover.go
index 1fe63e3ad..40c806fd7 100644
--- a/pkg/cover/cover.go
+++ b/pkg/cover/cover.go
@@ -17,6 +17,25 @@ func (cov *Cover) Merge(raw []uint32) {
 	}
 }
 
+// Merge merges raw into coverage and returns newly added PCs. Overwrites/mutates raw.
+func (cov *Cover) MergeDiff(raw []uint32) []uint32 {
+	c := *cov
+	if c == nil {
+		c = make(Cover)
+		*cov = c
+	}
+	n := 0
+	for _, pc := range raw {
+		if _, ok := c[pc]; ok {
+			continue
+		}
+		c[pc] = struct{}{}
+		raw[n] = pc
+		n++
+	}
+	return raw[:n]
+}
+
 func (cov Cover) Serialize() []uint32 {
 	res := make([]uint32, 0, len(cov))
 	for pc := range cov {
diff --git a/pkg/cover/cover_test.go b/pkg/cover/cover_test.go
new file mode 100644
index 000000000..7244ca186
--- /dev/null
+++ b/pkg/cover/cover_test.go
@@ -0,0 +1,64 @@
+// Copyright 2020 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package cover
+
+import (
+	"fmt"
+	"sort"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestMergeDiff(t *testing.T) {
+	type Test struct {
+		init   []uint32
+		merge  []uint32
+		diff   []uint32
+		result []uint32
+	}
+	tests := []Test{
+		{
+			init:   nil,
+			merge:  nil,
+			diff:   nil,
+			result: []uint32{},
+		},
+		{
+			init:   []uint32{0, 1, 3, 4},
+			merge:  nil,
+			diff:   nil,
+			result: []uint32{0, 1, 3, 4},
+		},
+		{
+			init:   nil,
+			merge:  []uint32{0, 1, 3, 4},
+			diff:   []uint32{0, 1, 3, 4},
+			result: []uint32{0, 1, 3, 4},
+		},
+		{
+			init:   []uint32{0, 1, 3, 4},
+			merge:  []uint32{4, 7, 1, 9},
+			diff:   []uint32{7, 9},
+			result: []uint32{0, 1, 3, 4, 7, 9},
+		},
+	}
+	for i, test := range tests {
+		t.Run(fmt.Sprint(i), func(t *testing.T) {
+			var cov Cover
+			cov.Merge(test.init)
+			diff := cov.MergeDiff(test.merge)
+			if res := cmp.Diff(test.diff, diff); res != "" {
+				t.Fatalf("MergeDiff result is wrong: %v", res)
+			}
+			result := cov.Serialize()
+			sort.Slice(result, func(i, j int) bool {
+				return result[i] < result[j]
+			})
+			if res := cmp.Diff(test.result, result); res != "" {
+				t.Fatalf("resulting coverage is wrong: %v", res)
+			}
+		})
+	}
+}