C++ base64加密解密

////////////////////////////////////////////////////////////
// base64.h

// 参考文章：http://www.cstc.net.cn/docs/docs.php?id=202

//************************************************************************/
//    base64编码表
// 
//  0 A 17 R 34 i 51 z 
//  1 B 18 S 35 j 52 0 
//  2 C 19 T 36 k 53 1 
//  3 D 20 U 37 l 54 2 
//  4 E 21 V 38 m 55 3 
//  5 F 22 W 39 n 56 4 
//  6 G 23 X 40 o 57 5 
//  7 H 24 Y 41 p 58 6 
//  8 I 25 Z 42 q 59 7 
//  9 J 26 a 43 r 60 8 
//  10 K 27 b 44 s 61 9 
//  11 L 28 c 45 t 62 + 
//  12 M 29 d 46 u 63 / 
//  13 N 30 e 47 v (pad) = 
//  14 O 31 f 48 w 
//  15 P 32 g 49 x 
//  16 Q 33 h 50 y 
//
// base64编码步骤：
// 
//  原文：
//
//  你好
//  C4 E3 BA C3
//  11000100 11100011 10111010 11000011
//  00110001 00001110 00001110 00111010
//  49       14       （十进制）
//  x        O        O        6  字符
//  01111000 01001111 01001111 00110110
//  78         （十六进制）
//  xOO6
//
//  解码：
//  xOO6
//  78 4f 4f 36
//  01111000 01001111 01001111 00110110
//  49       14 
//  00110001 00001110 00001110 00111010   31 0e 0e 3a
//
//  11000100 11100011 10111010
//  C4       E3       BA
//

#ifndef _BASE64_INCLUDE__H__
#define _BASE64_INCLUDE__H__

// 存储编码结果需要的长度，包含的长度
#define BASE64_ENCODE_LEN(A) ((A+2)/3 * 4 + 1)
// 存储解码结果需要的长度，包含的长度
#define BASE64_DECODE_LEN(A) (A / 4 * 3 + 2)

// 编码后的长度一般比原文多占1/3的存储空间，请保证base64code有足够的空间
inline int Base64Encode(char * base64code, const char * src, int src_len = 0); 
inline int Base64Decode(char * buf, const char * base64code, int src_len = 0);

__inline char GetB64Char(int index)
{
 const char szBase64Table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 if (index >= 0 && index < 64)
  return szBase64Table[index];
 
 return "=";
}

// 从双字中取单字节
#define B0(a) (a & 0xFF)
#define B1(a) (a >> 8 & 0xFF)
#define B2(a) (a >> 16 & 0xFF)
#define B3(a) (a >> 24 & 0xFF)

// 编码后的长度一般比原文多占1/3的存储空间，请保证base64code有足够的空间
inline int Base64Encode(char * base64code, const char * src, int src_len) 
{   
 if (src_len == 0)
  src_len = strlen(src);
 
 int len = 0;
 unsigned char* psrc = (unsigned char*)src;
 char * p64 = base64code;
 int i = 0;
 for (i = 0; i < src_len - 3; i += 3)
 {
  unsigned long ulTmp = *(unsigned long*)psrc;
  register int b0 = GetB64Char((B0(ulTmp) >> 2) & 0x3F); 
  register int b1 = GetB64Char((B0(ulTmp) << 6 >> 2 | B1(ulTmp) >> 4) & 0x3F); 
  register int b2 = GetB64Char((B1(ulTmp) << 4 >> 2 | B2(ulTmp) >> 6) & 0x3F); 
  register int b3 = GetB64Char((B2(ulTmp) << 2 >> 2) & 0x3F); 
  *((unsigned long*)p64) = b0 | b1 << 8 | b2 << 16 | b3 << 24;
  len += 4;
  p64  += 4; 
  psrc += 3;
 }
 
 // 处理最后余下的不足3字节的饿数据
 if (i < src_len)
 {
  int rest = src_len - i;
  unsigned long ulTmp = 0;
  for (int j = 0; j < rest; ++j)
  {
   *(((unsigned char*)&ulTmp) + j) = *psrc++;
  }
  
  p64[0] = GetB64Char((B0(ulTmp) >> 2) & 0x3F); 
  p64[1] = GetB64Char((B0(ulTmp) << 6 >> 2 | B1(ulTmp) >> 4) & 0x3F); 
  p64[2] = rest > 1 ? GetB64Char((B1(ulTmp) << 4 >> 2 | B2(ulTmp) >> 6) & 0x3F) : "="; 
  p64[3] = rest > 2 ? GetB64Char((B2(ulTmp) << 2 >> 2) & 0x3F) : "="; 
  p64 += 4; 
  len += 4;
 }
 
 *p64 = ""; 
 
 return len;
}


__inline int GetB64Index(char ch)
{
 int index = -1;
 if (ch >= "A" && ch <= "Z")
 {
  index = ch - "A";
 }
 else if (ch >= "a" && ch <= "z")
 {
  index = ch - "a" + 26;
 }
 else if (ch >= "0" && ch <= "9")
 {
  index = ch - "0" + 52;
 }
 else if (ch == "+")
 {
  index = 62;
 }
 else if (ch == "/")
 {
  index = 63;
 }

 return index;
}

// 解码后的长度一般比原文少用占1/4的存储空间，请保证buf有足够的空间
inline int Base64Decode(char * buf, const char * base64code, int src_len) 
{   
 if (src_len == 0)
  src_len = strlen(base64code);

 int len = 0;
 unsigned char* psrc = (unsigned char*)base64code;
 char * pbuf = buf;
 int i = 0;
 for (i = 0; i < src_len - 4; i += 4)
 {
  unsigned long ulTmp = *(unsigned long*)psrc;
  
  register int b0 = (GetB64Index((char)B0(ulTmp)) << 2 | GetB64Index((char)B1(ulTmp)) << 2 >> 6) & 0xFF;
  register int b1 = (GetB64Index((char)B1(ulTmp)) << 4 | GetB64Index((char)B2(ulTmp)) << 2 >> 4) & 0xFF;
  register int b2 = (GetB64Index((char)B2(ulTmp)) << 6 | GetB64Index((char)B3(ulTmp)) << 2 >> 2) & 0xFF;
  
  *((unsigned long*)pbuf) = b0 | b1 << 8 | b2 << 16;
  psrc  += 4; 
  pbuf += 3;
  len += 3;
 }

 // 处理最后余下的不足4字节的饿数据
 if (i < src_len)
 {
  int rest = src_len - i;
  unsigned long ulTmp = 0;
  for (int j = 0; j < rest; ++j)
  {
   *(((unsigned char*)&ulTmp) + j) = *psrc++;
  }
  
  register int b0 = (GetB64Index((char)B0(ulTmp)) << 2 | GetB64Index((char)B1(ulTmp)) << 2 >> 6) & 0xFF;
  *pbuf++ = b0;
  len  ++;

  if ("=" != B1(ulTmp) && "=" != B2(ulTmp))
  {
   register int b1 = (GetB64Index((char)B1(ulTmp)) << 4 | GetB64Index((char)B2(ulTmp)) << 2 >> 4) & 0xFF;
   *pbuf++ = b1;
   len  ++;
  }
  
  if ("=" != B2(ulTmp) && "=" != B3(ulTmp))
  {
   register int b2 = (GetB64Index((char)B2(ulTmp)) << 6 | GetB64Index((char)B3(ulTmp)) << 2 >> 2) & 0xFF;
   *pbuf++ = b2;
   len  ++;
  }

 }
  
 *pbuf = ""; 
 
 return len;
} 

#endif // #ifndef _BASE64_INCLUDE__H__