Algoritmo de cifrado y descifrado C / C ++ Base64

Práctico, también olvidé dónde lo copié, no hay problema en mi prueba, así que puedo ingresar directamente al proyecto.

const char base[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";   
/* Base64 编码 */   
char* base64_encode(const char* data, int data_len)   
{   
    //int data_len = strlen(data);   
    int prepare = 0;   
    int ret_len;   
    int temp = 0;   
    char *ret = NULL;   
    char *f = NULL;   
    int tmp = 0;   
    char changed[4];   
    int i = 0;   
    ret_len = data_len / 3;   
    temp = data_len % 3;   
    if (temp > 0)   
    {   
        ret_len += 1;   
    }   
    ret_len = ret_len*4 + 1;   
    ret = (char *)malloc(ret_len);   

    if ( ret == NULL)   
    {   
        printf("No enough memory.\n");   
        return nullptr;
    }   
    memset(ret, 0, ret_len);   
    f = ret;   
    while (tmp < data_len)   
    {   
        temp = 0;   
        prepare = 0;   
        memset(changed, '\0', 4);   
        while (temp < 3)   
        {   
            //printf("tmp = %d\n", tmp);   
            if (tmp >= data_len)   
            {   
                break;   
            }   
            prepare = ((prepare << 8) | (data[tmp] & 0xFF));   
            tmp++;   
            temp++;   
        }   
        prepare = (prepare<<((3-temp)*8));   
        //printf("before for : temp = %d, prepare = %d\n", temp, prepare);   
        for (i = 0; i < 4 ;i++ )   
        {   
            if (temp < i)   
            {   
                changed[i] = 0x40;   
            }   
            else   
            {   
                changed[i] = (prepare>>((3-i)*6)) & 0x3F;   
            }   
            *f = base[changed[i]];   
            //printf("%.2X", changed[i]);   
            f++;   
        }   
    }   
    *f = '\0';   

    return ret;   

}   

/* 转换算子 */   
static char find_pos(char ch)     
{   
    char *ptr = (char*)strrchr(base, ch);//the last position (the only) in base[]   
    return (ptr - base);   
}   

/* Base64 解码 */   
char* base64_decode(const char *data, int data_len)   
{   
    int ret_len = (data_len / 4) * 3;   
    int equal_count = 0;   
    char *ret = NULL;   
    char *f = NULL;   
    int tmp = 0;   
    int temp = 0;  
    int prepare = 0;   
    int i = 0;   
    if (*(data + data_len - 1) == '=')   
    {   
        equal_count += 1;   
    }   
    if (*(data + data_len - 2) == '=')   
    {   
        equal_count += 1;   
    }   
    if (*(data + data_len - 3) == '=')   
    {
   
   //seems impossible   
        equal_count += 1;   
    }   
    switch (equal_count)   
    {   
    case 0:   
        ret_len += 4;//3 + 1 [1 for NULL]   
        break;   
    case 1:   
        ret_len += 4;//Ceil((6*3)/8)+1   
        break;   
    case 2:   
        ret_len += 3;//Ceil((6*2)/8)+1   
        break;   
    case 3:   
        ret_len += 2;//Ceil((6*1)/8)+1   
        break;   
    }   
    ret = (char *)malloc(ret_len);   
    if (ret == NULL)   
    {   
        printf("No enough memory.\n");   
        return nullptr;
    }   
    memset(ret, 0, ret_len);   
    f = ret;   
    while (tmp < (data_len - equal_count))   
    {   
        temp = 0;   
        prepare = 0;   
        while (temp < 4)   
        {   
            if (tmp >= (data_len - equal_count))   
            {   
                break;   
            }   
            prepare = (prepare << 6) | (find_pos(data[tmp]));   
            temp++;   
            tmp++;   
        }   
        prepare = prepare << ((4-temp) * 6);   
        for (i=0; i<3 ;i++ )   
        {   
            if (i == temp)   
            {   
                break;   
            }   
            *f = (char)((prepare>>((2-i)*8)) & 0xFF);   
            f++;   
        }   
    }   
    *f = '\0';   
    return ret;   
}  

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