在C中实现bigint的最简单方法是什么？

#include<stdio.h>
#include <stdlib.h>
#include<string.h>
#include <stdbool.h>

#define MAX_DIGITS 1000

typedef struct {
    int digits[MAX_DIGITS];
    int len;
} BigInt;

void init_bigint(BigInt *a) {
    memset(a->digits, 0, sizeof(a->digits));
    a->len = 0;
}

void print_bigint(BigInt a) {
    for (int i = a.len - 1; i >= 0; i--) {
        printf("%d", a.digits[i]);
    }
    printf("\n");
}

void add_bigint(BigInt a, BigInt b, BigInt *result) {
    int carry = 0;
    int max_len = a.len > b.len ? a.len : b.len;
    for (int i = 0; i < max_len; i++) {
        int sum = a.digits[i] + b.digits[i] + carry;
        carry = sum / 10;
        result->digits[i] = sum % 10;
    }
    if (carry > 0) {
        result->digits[max_len++] = carry;
    }
    result->len = max_len;
}

void subtract_bigint(BigInt a, BigInt b, BigInt *result) {
    int borrow = 0;
    int max_len = a.len > b.len ? a.len : b.len;
    for (int i = 0; i < max_len; i++) {
        int diff = a.digits[i] - b.digits[i] - borrow;
        if (diff < 0) {
            diff += 10;
            borrow = 1;
        } else {
            borrow = 0;
        }
        result->digits[i] = diff;
    }
    int i = max_len;
    while (i < a.len && a.digits[i] != 0) {
        result->digits[i] = a.digits[i];
        i++;
    }
    result->len = i;
}

void multiply_bigint(BigInt a, BigInt b, BigInt *result) {
    memset(result->digits, 0, sizeof(result->digits));
    int max_len = a.len > b.len ? a.len : b.len;
    for (int i = 0; i < max_len; i++) {
        int carry = 0;
        for (int j = 0; j < max_len; j++) {
            int product = a.digits[i] * b.digits[j] + result->digits[i + j] + carry;
            carry = product / 10;
            result->digits[i + j] = product % 10;
        }
        if (carry > 0) {
            result->digits[max_len++] = carry;
        }
    }
    result->len = max_len;
}

bool is_zero(BigInt a) {
    for (int i = 0; i < a.len; i++) {
        if (a.digits[i] != 0) {
            return false;
        }
    }
    return true;
}

void divide_bigint(BigInt a, BigInt b, BigInt *quotient, BigInt *remainder) {
    memset(quotient->digits, 0, sizeof(quotient->digits));
    memset(remainder->digits, 0, sizeof(remainder->digits));
    for (int i = a.len - 1; i >= 0; i--) {
        remainder->digits[0] = a.digits[i];
        int divisor = remainder->digits[0];
        int quotient_digit = 0;
        while (divisor >= b.digits[b.len - 1]) {
            divisor -= b.digits[b.len - 1];
            quotient_digit++;
        }
        remainder->len = 1;
        BigInt temp;
        init_bigint(&temp);
        for (int j = b.len - 2; j >= 0; j--) {
            multiply_bigint(*remainder, 10, &temp);
            add_bigint(temp, *remainder, remainder);
            multiply_bigint(*remainder, 10, &temp);
            add_bigint(temp, *remainder, remainder);
            if (divisor == 0) {
                break;
            }
            if (remainder->len > b.len || remainder->digits[remainder->len - 1] >= b.digits[j]) {
                divisor -= b.digits[j];
                quotient_digit += b.digits[j];
                subtract_bigint(*remainder, b, remainder);
            }
        }
        quotient->digits[i] = quotient_digit;
    }
    quotient->len = a.len;
    while (quotient->len > 1 && quotient->digits[quotient->len - 1] == 0) {
        quotient->len--;
    }
    remainder->len = 1;
    while (remainder->len > 1 && remainder->digits[remainder->len - 1] == 0) {
        remainder->len--;
    }
}

int main() {
    BigInt a, b, result;
    init_bigint(&a);
    init_bigint(&b);
    init_bigint(&result);

    // 示例：123456789 * 987654321
    a.len = 9;
    for (int i = 0; i < 9; i++) {
        a.digits[i] = i + 1;
    }
    b.len = 9;
    for (int i = 0; i < 9; i++) {
        b.digits[i] = 9 - i;
    }

    multiply_bigint(a, b, &result);
    printf("Product of ");
    print_bigint(a);
    printf(" and ");
    print_bigint(b);
    printf(" is:\n");
    print_bigint(result);

    return 0;
}