Mul seems to be working

src/number/mul.rs

@@ -7,42 +7,43 @@ impl Mul for Number {
 
     #[allow(clippy::suspicious_arithmetic_impl)]
     fn mul(self, rhs: Self) -> Self::Output {
-        println!("left {self:#?}");
-        println!("right {rhs:#?}");
-        let mut mult_vecs = Vec::new();
         let sign = match (self.sign, rhs.sign) {
             (Sign::Positif, Sign::Positif) => Sign::Positif,
             (Sign::Positif, Sign::Negatif) => Sign::Negatif,
             (Sign::Negatif, Sign::Positif) => Sign::Negatif,
             (Sign::Negatif, Sign::Negatif) => Sign::Positif,
         };
-        for (idx, rdigit) in rhs.digits.iter().enumerate() {
-            let rdigit = rdigit * 10_isize.pow(idx as u32);
-            let mult_vec: Vec<isize> = self.digits.iter().map(|ldigit| ldigit * rdigit).collect();
-            let mut normalized_mult_vec = Vec::new();
-            let mut carry = 0;
-            let mut add_zero = true;
-            mult_vec.into_iter().for_each(|digit| {
-                let digit = digit + carry;
-                if digit > 9 {
-                    carry = digit % 10;
-                    normalized_mult_vec.insert(0, digit / 10);
+        let mut digits = Vec::new();
+        for (zeroes, rdigit) in rhs.digits.iter().enumerate() {
+            for (idx, ldigit) in self.digits.iter().enumerate() {
+                let mult = rdigit * ldigit;
+                let new = mult % 10;
+                let mut carry = mult / 10;
+                if let Some(old) = digits.get(zeroes + idx) {
+                    let add = old + new;
+                    digits[zeroes + idx] = add % 10;
+                    carry += add / 10;
                 } else {
-                    normalized_mult_vec.insert(0, digit);
-                    carry = 0;
-                    add_zero = false;
+                    digits.push(new);
+                }
+                let mut carry_idx = 1;
+                loop {
+                    if carry == 0 {
+                        break;
+                    }
+                    if let Some(old) = digits.get(zeroes + idx + carry_idx) {
+                        let add = old + carry;
+                        digits[zeroes + idx + carry_idx] = add % 10;
+                        carry = add / 10;
+                    } else {
+                        digits.push(carry % 10);
+                        carry /= 10;
+                    }
+                    carry_idx += 1;
                 }
-            });
-            if carry != 0 || add_zero {
-                normalized_mult_vec.insert(0, carry);
             }
-            mult_vecs.push(Number {
-                digits: normalized_mult_vec,
-                sign,
-            });
         }
-
-        mult_vecs.into_iter().reduce(|acc, num| acc + num).unwrap()
+        Number { digits, sign }
     }
 }
 
@@ -123,7 +124,15 @@ mod test_number_mul {
     }
 
     #[test]
-    fn mul_big() {
+    fn mul_big_1() {
+        let a = Number::from("123");
+        let b = Number::from("321");
+        let res = Number::from("39483");
+        assert_eq!(res, a * b);
+    }
+
+    #[test]
+    fn mul_big_2() {
         let a = Number::from("123456789");
         let b = Number::from("987654321");
         let res = Number::from("121932631112635269");