Our team developed the following base 64 encoding routine to encode bitmap images to be sent over the internet. When the encoded file reaches the email destination, the header is mangled and the colors of the bitmap are altered.

We are trying to track down whether it is the encoding code that has a flaw, or whether the TCP/IP code is mangling the file. Does anyone see any problems with the following code?

#include "WrNet.h"

signed long b64chunk(unsigned long ibuf, unsigned long obuf, signed char number){
  unsigned long temp;
  char* in = (char *)ibuf;
  char* out = (char *)obuf;
  char* base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789/+";

  if (number >= 1)
    temp = in[0] * 65536;
  if (number >= 2)
    temp = temp + in[1] * 256;
  if (number == 3)
	temp = temp + in[2];
	
  out[3] = base64[((temp % 64))];
  out[2] = base64[((temp % 4096) / 64)];
  out[1] = base64[((temp % 262144) / 4096)];
  out[0] = base64[((temp % 16777216) / 262144)];

  if(number < 3)
    out[3] = '=';
  if(number < 2)
    out[2] = '=';

  return 0;
}

signed long b64line(unsigned long ibuf, unsigned long obuf, signed char number){
  unsigned int offset = 0;
  unsigned int outchars = 0;
  char* out = (char *)obuf;

  if (number > 57)
    number = 57;

  while (number > offset) {
    if ((number - offset) >= 3) {
      b64chunk(ibuf + offset, obuf + outchars, 3);
      offset = offset + 3;
      outchars = outchars + 4;
    } else {
      b64chunk(ibuf + offset, obuf + outchars, (number - offset));
      offset = number;
      outchars = outchars + 4;
    }
  }
  out[outchars] = '\n';
  out[outchars+1] = '\0';
  return 0;
}