C++ VC Base64編解碼演算法系列二(編碼演算法)

void base64_encode(char *out, const void *in_, int inlen)

/* raw bytes in quasi-big-endian order to base 64 string (NUL-terminated) */
 
{
  const unsigned char *in = (const unsigned char *)in_;
  for (; inlen >= 3; inlen -= 3) 
  {
    *out++ = base64digits[in[0] >> 2];
    *out++ = base64digits[((in[0] << 4) & 0x30) | (in[1] >> 4)];
    *out++ = base64digits[((in[1] << 2) & 0x3c) | (in[2] >> 6)];
    *out++ = base64digits[in[2] & 0x3f];
    in += 3;
  }
  if (inlen > 0) 
  {
    unsigned char fragment;
    *out++ = base64digits[in[0] >> 2];
    fragment = (in[0] << 4) & 0x30;
    if (inlen > 1)  fragment |= in[1] >> 4;
    *out++ = base64digits[fragment];
    *out++ = (inlen < 2) ? '=' : base64digits[(in[1] << 2) & 0x3c];
    *out++ = '=';
  }
  *out = '/0';
}