ConvertBBCode

const char __attribute__ ((hot)) *ConvertBBCode(char *Output, const char *Input, int BufSize) {
  if(!strchr(Input, '[')) return Input; // no conversion necessary

  const char *TagName[] = {"b]","i]","u]","s]","sub]","sup]","url=","url]","icon]","user]","color=","color]","noparse]",NULL};
  const int TagLen[] = {2, 2, 2, 2, 4, 4, 4, 4, 5, 5, 6, 6, 8}; // 5+ treated specially
  const char *TagEndName[] = {"[/b]","[/i]","[/u]","[/s]","[/sub]","[/sup]","[/url]","[/url]","[/icon]","[/user]","[/color]",NULL,"[/noparse]"};
  const int TagCodes[] = {0x02, 0x1d, 0x1f, 128+FORMAT_STRIKEOUT, 128+FORMAT_SUBSCRIPT, 128+FORMAT_SUPERSCRIPT,
    128+FORMAT_URL_LINK, 128+FORMAT_URL_LINK, 128+FORMAT_ICON_CMDLINK, 128+FORMAT_COMMAND_LINK,
    128+FORMAT_CANCEL_COLORS, 128+FORMAT_CANCEL_COLORS};
  int TagEnabled[] = {0,0,0,0,0,0,0,0,0,0,0,0,0};
  char *Out = Output;
  int i; // tag index to try

  while(*Input) {
    char c = *(Input++);
    if(c != '[') // if not [ just copy it
      *(Out++) = c;
    else
      if(*Input == '/') { // cancel formatting
        for(i=0;TagName[i];i++)
          if(!memcmp(Input+1, TagName[i], TagLen[i])) {
            if(TagEnabled[i]) {
              Input+=TagLen[i]+1;
              if(TagCodes[i] & 128) // need escape code?
                *(Out++) = 0xff;
              *(Out++) = TagCodes[i]&127;
              TagEnabled[i] = 0;
            } else {
              *(Out++) = '['; // tag isn't enabled, print it
            }
            break;
          }
        if(!TagName[i]) // put the [ if not a valid tag
          *(Out++) = '[';
      } else { // start formatting
        for(i=0;TagName[i];i++)
          if(!memcmp(Input, TagName[i], TagLen[i])) {
            if(!TagEndName[i] || !strstr(Input, TagEndName[i])) { // if tag isn't closed, tag should be visible
              *(Out++) = '['; // add the [ back
              break;
            }
            Input+=TagLen[i];
            if(TagLen[i] < 6) { // 6+ handle outputting on their own
              if(TagCodes[i] & 128) // need escape code?
                *(Out++) = 0xff;
              *(Out++) = TagCodes[i]&127;
              if(i!=6)
                TagEnabled[i] = 1;
              else // url= has to set url]
                TagEnabled[i+1] = 1;
            }
            // special handling for lengths of at least 5
            if(TagLen[i]>=5) {
              if(TagLen[i]==5) { // [icon] or [user], stick in a command name
                strcpy(Out, "char ");
                Out+=5;
              } else if(TagLen[i]==6) { // [color]
                const char *End = strchr(Input, ']');
                char ColorName[End-Input+1];
                strlcpy(ColorName, Input, sizeof(ColorName));
                Input = End+1;
                if(*ColorName == '#') { // hex color
                  *(Out++) = 0x04;
                  if(strlen(ColorName) == 4) { // convert 3 digit to 6 digit
                    for(int j=1;j<4;j++) { // double every digit
                      *(Out++)=ColorName[j];
                      *(Out++)=ColorName[j];
                    }
                  } else { // assume 6 digits
                    strcpy(Out, ColorName+1);
                    Out+=6;
                  }
                } else {
                  for(int j=0;FChatColorNames[j];j++)
                    if(!strcasecmp(ColorName, FChatColorNames[j])) {
                      sprintf(ColorName, "\3%.2d", j+16); // F-Chat colors start at 16
                      strcpy(Out, ColorName);
                      Out+=3;
                      break;
                    }
                }
                TagEnabled[i+1] = 1;
              } else { // [noparse]
                const char *End = strstr(Input, "[/noparse]");
                memcpy(Out, Input, End-Input);
                Out+=(End-Input)+10;
              }
            }
            break;
          }
        if(!TagName[i]) // put the [ if not a valid tag
          *(Out++) = '[';
      }
  }
  *Out = 0;
  return Output;
}