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来源：互联网发布：安卓电商app源码编辑：程序博客网时间：2024/04/28 20:58

// 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;

unsigned long ulTmp = 0;

for (int j = 0; j < src_len - 4; ++j)
{
*(((unsigned char*)&ulTmp) + j) = *psrc++;
}
for (int i = 0; i < src_len - 4; i += 4)
{
//unsigned long ulTmp = (unsigned long )psrc;

  //*((unsigned char*)&ulTmp + 3) = *psrc++;
  register int b0 = (GetB64Index((char)B0(ulTmp)) << 2 | GetB64Index((char)B1(ulTmp)) << 2 >> 6) & 0xFF;
  *pbuf++ = b0 ;
  len ++;

  //*((unsigned char*)&ulTmp + 2) = *psrc++ ;
  register int b1 = (GetB64Index((char)B1(ulTmp)) << 4 | GetB64Index((char)B2(ulTmp)) << 2 >> 4) & 0xFF;
  *pbuf++ = b1;
  len ++;

  //*((unsigned char*)&ulTmp + 1) = *psrc++ ;
  register int b2 = (GetB64Index((char)B2(ulTmp)) << 6 | GetB64Index((char)B3(ulTmp)) << 2 >> 2) & 0xFF;
  *pbuf++ = b2;
  len ++;
  //*((unsigned char*)&ulTmp + 3) = *psrc++ ;
}

// 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 = '/0';

return len;
}