base64編解碼的兩個函數

base64編解碼的兩個函數，聲明，參考網絡上的代碼實現。

unsigned char *base64_encode(unsigned char *str, long* lpBufLen)  
{  
    long len;  
    long str_len;  
    unsigned char *res;  
    int i,j;  
//定義base64編碼表  
	const unsigned char *base64_table = (const unsigned char *)("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");  
  
//計算經過base64編碼后的字符串長度  
    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個8位字符為一組進行編碼  
    for(i=0,j=0;i<len-2;j+=3,i+=4)  
    {  
        res[i]=base64_table[str[j]>>2]; //取出第一個字符的前6位並找出對應的結果字符  
        res[i+1]=base64_table[(str[j]&0x3)<<4 | (str[j+1]>>4)]; //將第一個字符的后位與第二個字符的前4位進行組合並找到對應的結果字符  
        res[i+2]=base64_table[(str[j+1]&0xf)<<2 | (str[j+2]>>6)]; //將第二個字符的后4位與第三個字符的前2位組合並找出對應的結果字符  
        res[i+3]=base64_table[str[j+2]&0x3f]; //取出第三個字符的后6位並找出結果字符  
    }  
  
    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)  
{  
//根據base64表，以字符找到對應的十進制數據  
    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;  
  
//計算解碼后的字符串長度  
    len=strlen((char*)code);  
//判斷編碼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個字符為一位進行解碼  
    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); //取出第一個字符對應base64表的十進制數的前6位與第二個字符對應base64表的十進制數的后2位進行組合  
        res[j+1]=(((unsigned char)table[code[i+1]])<<4) | (((unsigned char)table[code[i+2]])>>2); //取出第二個字符對應base64表的十進制數的后4位與第三個字符對應bas464表的十進制數的后4位進行組合  
        res[j+2]=(((unsigned char)table[code[i+2]])<<6) | ((unsigned char)table[code[i+3]]); //取出第三個字符對應base64表的十進制數的后2位與第4個字符進行組合  
    }  
  
    return res;  
  
}