Add SafeDivBig

pkg/utils/math_utils.go

@@ -2,6 +2,7 @@ package utils
 
 import (
 	"math"
+	"math/big"
 
 	"github.com/pkg/errors"
 )
@@ -50,3 +51,15 @@ func DivCeil(x uint, y uint) uint {
 	}
 	return q
 }
+
+// Performs integer division between x and y; fails if x is not divisible by y.
+func SafeDivBig(x *big.Int, y *big.Int) (*big.Int, error) {
+	if y.Cmp(big.NewInt(0)) == 0 {
+		return &big.Int{}, errors.New("SafeDiv: Attempted to divide by zero")
+	}
+	q, r := x.DivMod(x, y, new(big.Int))
+	if r.Cmp(big.NewInt(0)) != 0 {
+		return &big.Int{}, errors.Errorf("SafeDiv: %s is not divisible by %s", x.Text(10), y.Text(10))
+	}
+	return q, nil
+}

pkg/utils/math_utils_test.go

@@ -0,0 +1,46 @@
+package utils_test
+
+import (
+	"math/big"
+	"testing"
+
+	. "github.com/lambdaclass/cairo-vm.go/pkg/utils"
+)
+
+func TestSafeDivBigOkSmallNumbers(t *testing.T) {
+	a := big.NewInt(10)
+	b := big.NewInt(5)
+	expected := big.NewInt(2)
+	val, err := SafeDivBig(a, b)
+	if err != nil || val.Cmp(expected) != 0 {
+		t.Error("Wrong value returned by SafeDivBig")
+	}
+}
+
+func TestSafeDivBigOkBigNumbers(t *testing.T) {
+	a, _ := new(big.Int).SetString("1354671610274991796869769298862800192014", 10)
+	b, _ := new(big.Int).SetString("37853847583", 10)
+	expected, _ := new(big.Int).SetString("35786893453952854863476753458", 10)
+	val, err := SafeDivBig(a, b)
+	if err != nil || val.Cmp(expected) != 0 {
+		t.Error("Wrong value returned by SafeDivBig")
+	}
+}
+
+func TestSafeDivBigErrNotDivisible(t *testing.T) {
+	a := big.NewInt(10)
+	b := big.NewInt(7)
+	_, err := SafeDivBig(a, b)
+	if err == nil {
+		t.Error("SafeDivBig should have failed")
+	}
+}
+
+func TestSafeDivBigErrZeroDivison(t *testing.T) {
+	a := big.NewInt(10)
+	b := big.NewInt(0)
+	_, err := SafeDivBig(a, b)
+	if err == nil {
+		t.Error("SafeDivBig should have failed")
+	}
+}