codec/h264/h264dec: wrote UnaryBinarization function and TestUnaryBinarization

codec/h264/h264dec/cabac.go

@@ -733,3 +733,21 @@ func CtxIdx(binIdx, maxBinIdxCtx, ctxIdxOffset int) int {
 
 	return ctxIdx
 }
+
+// Error used by unaryBinarization.
+var errNegativeSyntaxVal = errors.New("cannot get unary binarization of negative value")
+
+// unaryBinarization returns the unary binarization of a syntax element having
+// value v, as specified by setion 9.3.2.1 in the specifications.
+func unaryBinarization(v int) ([]int, error) {
+	if v < 0 {
+		return nil, errNegativeSyntaxVal
+	}
+	r := make([]int, v+1)
+	for i := 0; i <= v; i++ {
+		if i < v {
+			r[i] = 1
+		}
+	}
+	return r, nil
+}

codec/h264/h264dec/cabac_test.go

@@ -186,3 +186,31 @@ func TestCtxIdx(t *testing.T) {
 		}
 	}
 }
+
+func TestUnaryBinarization(t *testing.T) {
+	// Test data has been extracted from table 9-35 of the specifications.
+	tests := []struct {
+		in   int
+		want []int
+		err  error
+	}{
+		{in: 0, want: []int{0}, err: nil},
+		{in: 1, want: []int{1, 0}, err: nil},
+		{in: 2, want: []int{1, 1, 0}, err: nil},
+		{in: 3, want: []int{1, 1, 1, 0}, err: nil},
+		{in: 4, want: []int{1, 1, 1, 1, 0}, err: nil},
+		{in: 5, want: []int{1, 1, 1, 1, 1, 0}, err: nil},
+		{in: -3, want: nil, err: errNegativeSyntaxVal},
+	}
+
+	for i, test := range tests {
+		got, err := unaryBinarization(test.in)
+		if err != test.err {
+			t.Errorf("did not get expected error for test %d\nGot: %v\nWant: %v", i, err, test.err)
+		}
+
+		if !reflect.DeepEqual(test.want, got) {
+			t.Errorf("did not get expected result for test %d\nGot: %v\nWant: %v\n", i, got, test.want)
+		}
+	}
+}