无符号大数相加(C语言实现)

1. 请用自己熟悉的语言，实现无符号大数加法操作。
   a. 完成两个大数的加法 A + B = C，并正确处理进位情况;
   b. 成功返回0，失败返回-1
   c. 各个大数用无符号字节数组表示。
   d. C语言接口说明如下
   int bignum_add(uint8_t* pA, int aLen, uint8_t* pB, int bLen, uint8_t* pC, int* cLen);

   举例:
   uint8_t A[] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x22, 0x33, 0x44};
   uint8_t B[] = {0x33, 0x44};
   //结果输出为: {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x22, 0x66, 0x88}

/*************************************************************************
    > File Name: integer_add.c
    > Author: killshadow
    > Mail: chaceli@foxmail.com
    > Created Time: 2021-8-4
 ************************************************************************/

#include <stdio.h>
#include <stdint.h>

#define MAX_LEN 100

/**
 * Add big num function.
 *
 * @param pA first big num.
 * @param aLen first big num len.
 * @param pB second big num.
 * @param bLen second big num len.
 * @param pC calculate result big num.
 * @param cLen calculate result big num len.
 * @return {@code 0} calculate success.
 */
int bignum_add(uint8_t* pA, int aLen, uint8_t* pB, int bLen, uint8_t* pC, int* cLen);

/**
 * Print byte array.
 *
 * @param arr
 * @param length
 */
void print_arr(uint8_t *arr, int length);

/**
 * Reverse array
 * @param arr input array.
 * @param length input array len.
 */
void reverse_arr(uint8_t* arr, int length);

/**
 * Fill array with 0xFF by start index.
 * @param arr input array.
 * @param start start index.
 * @param length array length.
 */
void fill_arr(uint8_t* arr, int start, int length);

int bignum_add(uint8_t* pA, int aLen, uint8_t* pB, int bLen, uint8_t* pC, int* cLen)
{
    if ((pA == NULL) || (aLen <= 0) || (pB == NULL) || (bLen <= 0) || (pC == NULL)) {
        return -1;
    }
    int carry = 0;
    int tmp;
    int idx;
    int long_len;
    int short_len;
    if (aLen >= bLen) {
        long_len = aLen;
        short_len = bLen;
    } else {
        long_len = bLen;
        short_len = aLen;
    }

    reverse_arr(pA, aLen);
    reverse_arr(pB, bLen);

    for (idx = 0; idx < short_len; idx++) {
        tmp = pA[idx] + pB[idx] + carry;
        pC[idx] = tmp % 0xFF;
        carry = tmp / 0xFF;
    }

    if (carry != 0) {
        pC[idx] = carry;
        *cLen = long_len + 1;
    } else {
        *cLen = long_len;
    }
    return 0;
}

void print_arr(uint8_t *arr, int length) {
    for (int i = length - 1; i >= 0; i--) {
        printf("0x%x ", arr[i]);
    }
    puts("\n");
}

void reverse_arr(uint8_t *arr, int length) {
    int left = 0;
    int right = length - 1;
    while (left < right) {
        int tmp = arr[right];
        arr[right--] = arr[left];
        arr[left++] = tmp;
    }
}

void fill_arr(uint8_t* arr, int start, int length)
{
    for (int i = start; i < length; ++i) {
        arr[i] = 0xFF;
    }
}

int main()
{
    uint8_t A[] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x22, 0x33, 0x44};
    int aLen = sizeof(A) / sizeof(uint8_t);
    uint8_t B[] = {0x33, 0x44};
    int bLen = sizeof(B) / sizeof(uint8_t);
    // {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x22, 0x66, 0x88}
    uint8_t C[MAX_LEN] = {0xFF};
    fill_arr(C, 0, MAX_LEN);
    int cLen = 0;
    bignum_add(A, aLen, B, bLen, C, &cLen);
    print_arr(C, cLen);
    return 0;
}