feat: Big num for state representation

bignum.c

@@ -0,0 +1,41 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include "bignum.h"
+
+struct BigNum long_to_BigNum(long long num) {
+    struct BigNum ans;
+    int temp;
+    for (int i=BIGNUM_LEN-1; i>=0; i--) {
+        temp = num % 10;
+        num /= 10;
+        ans.num[i] = (char)(temp + 48);
+    }
+    return ans;
+}
+
+struct BigNum add(struct BigNum a, struct BigNum b) {
+    struct BigNum ans;
+    bool carry;
+    short s;
+    for (short i=BIGNUM_LEN-1; i>=0; i--) {
+        s = (a.num[i]-48) + (b.num[i]-48) + carry;
+        carry = s / 10;
+        s %= 10;
+        ans.num[i] = (char)(s+48);
+    }
+    return ans;
+}
+
+struct BigNum mul(struct BigNum a, int b) {
+    struct BigNum ans;
+    short s, carry;
+
+    for (short i=BIGNUM_LEN-1; i>=0; i--) {
+        s = (a.num[i]-48) * b + carry;
+        carry = s / 10;
+        s %= 10;
+        ans.num[i] = (char)(s+48);
+    }
+
+    return ans;
+}

bignum.h

@@ -0,0 +1,7 @@
+#include "constant.h"
+struct BigNum {
+    char num[BIGNUM_LEN];
+};
+struct BigNum long_to_BigNum(long long num);
+struct BigNum add(struct BigNum a, struct BigNum b);
+struct BigNum mul(struct BigNum a, int b);