base64.c

static char *b64chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

int base64_encode(const unsigned char *data, int len, char *dest)
{
  char *buf = dest;

  /* Encode 3 bytes at a time. */
  while (len >= 3) {
    buf[0] = b64chars[(data[0] >> 2) & 0x3f];
    buf[1] = b64chars[((data[0] << 4) & 0x30) | ((data[1] >> 4) & 0xf)];
    buf[2] = b64chars[((data[1] << 2) & 0x3c) | ((data[2] >> 6) & 0x3)];
    buf[3] = b64chars[data[2] & 0x3f];
    data += 3;
    buf += 4;
    len -= 3;
  }

  if (len > 0) {
    buf[0] = b64chars[(data[0] >> 2) & 0x3f];
    buf[1] = b64chars[(data[0] << 4) & 0x30];
    if (len > 1) {
      buf[1] += (data[1] >> 4) & 0xf;
      buf[2] = b64chars[(data[1] << 2) & 0x3c];
    }
    else buf[2] = '=';
    buf[3] = '=';
    buf += 4;
  }

  *buf = '\0';
  return(buf - dest);
}

int base64_decode(const unsigned char *data, int len, char *dest)
{
  unsigned char c;
  int cur = 0, val = 0, i = 0;

  while (len) {
    c = *data;
    len--;
    data++;

    if (c >= 'A' && c <= 'Z') val = c - 'A';
    else if (c >= 'a' && c <= 'z') val = c - 'a' + 26;
    else if (c >= '0' && c <= '9') val = c - '0' + 52;
    else if (c == '+') val = 62;
    else if (c == '/') val = 63;
    else if (c == '=') break;
    else continue;

    switch (cur++) {
      case 0:
        dest[i] = (val << 2) & 0xfc;
        break;
      case 1:
        dest[i] |= (val >> 4) & 0x03;
        i++;
        dest[i] = (val << 4) & 0xf0;
        break;
      case 2:
        dest[i] |= (val >> 2) & 0x0f;
        i++;
        dest[i] = (val << 6) & 0xc0;
        break;
      case 3:
        dest[i] |= val & 0x3f;
        i++;
        cur = 0;
        break;
    }
  }
  dest[i] = 0;
  return(i);
}