unit-tests + fix

Signed-off-by: Angelo De Caro <adc@zurich.ibm.com>

Author: adecaro

driver/common/curve.go

@@ -101,7 +101,7 @@ func (p *CurveBase) Rand() (io.Reader, error) {
 func (p *CurveBase) ModAddMul(a1 []driver.Zr, b1 []driver.Zr, modulo driver.Zr) driver.Zr {
 	sum := p.NewZrFromInt64(0)
 	for i := 0; i < len(a1); i++ {
-		p.ModAdd(sum, p.ModMul(a1[i], b1[i], modulo), modulo)
+		sum = p.ModAdd(sum, p.ModMul(a1[i], b1[i], modulo), modulo)
 	}
 	return sum
 }

math_test.go

@@ -540,6 +540,18 @@ func runModAddSubNegTest(t *testing.T, c *Curve) {
 	apb := c.ModAdd(a, b, c.GroupOrder)
 	bagain := c.ModSub(apb, a, c.GroupOrder)
 	assert.True(t, bagain.Equals(b))
+
+	a2 := c.NewRandomZr(rng)
+	b2 := c.NewRandomZr(rng)
+
+	v := c.ModAddMul2(a, b, a2, b2, c.GroupOrder)
+	atb := c.ModMul(a, b, c.GroupOrder)
+	a2tb2 := c.ModMul(a2, b2, c.GroupOrder)
+	v2 := c.ModAdd(atb, a2tb2, c.GroupOrder)
+	assert.True(t, v.Equals(v2))
+
+	v3 := c.ModAddMul([]*Zr{a, a2}, []*Zr{b, b2}, c.GroupOrder)
+	assert.True(t, v.Equals(v3))
 }
 
 func runMulTest(t *testing.T, c *Curve) {