nancygold's Journal

Going further...
During the initialization stage, the game calls function 1600h of the `int 2fh`.

//virtual dos machine interface 0x2F:0x1600 interrupt results
#define VDM_NONE      0
#define VDM_OTHER_VM  0x01
#define VDM_SYSTEM_VM 0xFF
#define VDM_HIMEM_SYS 0x80
#define NO_VDM(r) ((r)==VDM_NONE || (r) == VDM_HIMEM_SYS)
uint8_t vdm_query() {
  asm {
    mov ax, 0x1600
    int 0x2f
    xor ah, ah
  }
  return _AL;
}

That interrupt is very special, and the function 1600h is even more special.
Basically the game checks for the presence of Windows 3.1, and configures the PC Speaker accordingly
https://www.geoffchappell.com/notes/dos/interrupts/2Fh/16h/00h.htm

Here is another gem...

//again, crufty code with '}' repeating two times...
//BTW, Borland C++ 3.0 ctype.h had isprint(c)
byte is_printable(char *buf, char c) {
  UNUSED(buf);
  return isalnum(c) || c == ':' || c == '.' || c == '\\' || c == '}' || c == '!'
    || c == '@' || c == '#' || c == '$' || c == '%' || c == '^' || c == '&'
    || c == '(' || c == ')' || c == '-' || c == '_' || c == '{' || c == '}'
    || c == '~' || c == '`';
}

Current Mood: amused