base64编解码的两个函数

base64编解码的两个函数，声明，参考网络上的代码实现。

unsigned char *base64_encode(unsigned char *str, long* lpBufLen)
{
    long len;
    long str_len;
    unsigned char *res;
    int i,j;
//定义base64编码表
	const unsigned char *base64_table = (const unsigned char *)("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");  

//计算经过base64编码后的字符串长度
    str_len=strlen((char*)str);
    if(str_len % 3 == 0)
        len=str_len/3*4;
    else
        len=(str_len/3+1)*4;

	if (NULL != lpBufLen) {
		*lpBufLen = len;
	}

    res = (unsigned char *)malloc(sizeof(unsigned char)*len+1);
    res[len]='\0';  

//以3个8位字符为一组进行编码
    for(i=0,j=0;i<len-2;j+=3,i+=4)
    {
        res[i]=base64_table[str[j]>>2]; //取出第一个字符的前6位并找出对应的结果字符
        res[i+1]=base64_table[(str[j]&0x3)<<4 | (str[j+1]>>4)]; //将第一个字符的后位与第二个字符的前4位进行组合并找到对应的结果字符
        res[i+2]=base64_table[(str[j+1]&0xf)<<2 | (str[j+2]>>6)]; //将第二个字符的后4位与第三个字符的前2位组合并找出对应的结果字符
        res[i+3]=base64_table[str[j+2]&0x3f]; //取出第三个字符的后6位并找出结果字符
    }  

    switch(str_len % 3)
    {
        case 1:
            res[i-2]='=';
            res[i-1]='=';
            break;
        case 2:
            res[i-1]='=';
            break;
    }

    return res;
}

unsigned char *base64_decode(unsigned char *code, long* lpBufLen)
{
//根据base64表，以字符找到对应的十进制数据
    int table[]={0,0,0,0,0,0,0,0,0,0,0,0,
    		 0,0,0,0,0,0,0,0,0,0,0,0,
    		 0,0,0,0,0,0,0,0,0,0,0,0,
    		 0,0,0,0,0,0,0,62,0,0,0,
    		 63,52,53,54,55,56,57,58,
    		 59,60,61,0,0,0,0,0,0,0,0,
    		 1,2,3,4,5,6,7,8,9,10,11,12,
    		 13,14,15,16,17,18,19,20,21,
    		 22,23,24,25,0,0,0,0,0,0,26,
    		 27,28,29,30,31,32,33,34,35,
    		 36,37,38,39,40,41,42,43,44,
    		 45,46,47,48,49,50,51
    	       };
    long len;
    long str_len;
    unsigned char *res;
    int i,j;  

//计算解码后的字符串长度
    len=strlen((char*)code);
//判断编码后的字符串后是否有=
    if(strstr((char*)code,"=="))
        str_len=len/4*3-2;
    else if(strstr((char*)code,"="))
        str_len=len/4*3-1;
    else
        str_len=len/4*3;  

	if (NULL != lpBufLen) {
		*lpBufLen = str_len;
	}

    res=(unsigned char*)malloc(sizeof(unsigned char)*str_len+1);
    res[str_len]='\0';  

//以4个字符为一位进行解码
    for(i=0,j=0;i < len-2;j+=3,i+=4)
    {
        res[j]=((unsigned char)table[code[i]])<<2 | (((unsigned char)table[code[i+1]])>>4); //取出第一个字符对应base64表的十进制数的前6位与第二个字符对应base64表的十进制数的后2位进行组合
        res[j+1]=(((unsigned char)table[code[i+1]])<<4) | (((unsigned char)table[code[i+2]])>>2); //取出第二个字符对应base64表的十进制数的后4位与第三个字符对应bas464表的十进制数的后4位进行组合
        res[j+2]=(((unsigned char)table[code[i+2]])<<6) | ((unsigned char)table[code[i+3]]); //取出第三个字符对应base64表的十进制数的后2位与第4个字符进行组合
    }  

    return res;  

}