Add method to export Zr to unsigned int

Resolves #20

Signed-off-by: Alessandro Sorniotti <aso@zurich.ibm.com>

Author: ale-linux

math.go

@@ -232,6 +232,15 @@ func (z *Zr) Neg() {
 var zerobytes = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
 var onebytes = []byte{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
 
+func (z *Zr) Uint() (uint64, error) {
+	b := z.Bytes()
+	if !bytes.Equal(zerobytes, b[:32-8]) && !bytes.Equal(onebytes, b[:32-8]) {
+		return 0, fmt.Errorf("out of range")
+	}
+
+	return uint64(binary.BigEndian.Uint64(b[32-8:])), nil
+}
+
 func (z *Zr) Int() (int64, error) {
 	b := z.Bytes()
 	if !bytes.Equal(zerobytes, b[:32-8]) && !bytes.Equal(onebytes, b[:32-8]) {

math_test.go

@@ -126,6 +126,33 @@ func runZrTest(t *testing.T, c *Curve) {
 
 	maxint64 := c.NewZrFromInt(math.MaxInt64)
 	maxuint64 := c.NewZrFromUint64(math.MaxUint64)
+
+	iu, err := maxint64.Uint()
+	assert.NoError(t, err)
+	assert.Equal(t, uint64(math.MaxInt64), iu)
+
+	i64, err := maxint64.Int()
+	assert.NoError(t, err)
+	assert.Equal(t, int64(math.MaxInt64), i64)
+
+	ui, err := maxuint64.Int()
+	assert.NoError(t, err)
+	assert.Equal(t, int64(-1), ui)
+
+	u64, err := maxuint64.Uint()
+	assert.NoError(t, err)
+	assert.Equal(t, uint64(math.MaxUint64), u64)
+
+	a, b := rand.Int63(), rand.Int63()
+	cr, err := c.NewZrFromInt(a).Plus(c.NewZrFromInt(b)).Int()
+	assert.NoError(t, err)
+	assert.Equal(t, a+b, cr)
+
+	au, bu := uint64(rand.Int63()), uint64(rand.Int63())
+	cru, err := c.NewZrFromUint64(au).Plus(c.NewZrFromUint64(bu)).Uint()
+	assert.NoError(t, err)
+	assert.Equal(t, au+bu, cru)
+
 	assert.Equal(t, fmt.Sprintf("%x", math.MaxInt64), maxint64.String())
 	assert.Equal(t, fmt.Sprintf("%x", uint64(math.MaxUint64)), maxuint64.String())
 
@@ -150,7 +177,7 @@ func runZrTest(t *testing.T, c *Curve) {
 
 	rand.Seed(seed)
 
-	i64 := rand.Int63()
+	i64 = rand.Int63()
 	i = c.NewZrFromInt(i64)
 	i64_, err := i.Int()
 	assert.NoError(t, err)