#borlandcpp — Public Fediverse posts

90s setup programs are creative as heck #borlandcpp

The Dark Art of DOS Audio: PC Speaker Tricks and PWM Madness
Think the old PC speaker was only good for making awful beeps? Yeah, me too—until I started digging into how it actually works.#MSDOS #BorlandCPP #RetroCoding #DOSDev #chiptune
https://ncot.uk/videos/the-dark-art-of-dos-audio-pc-speaker-tricks-and-pwm-madness/

This appears to be the minimal configuration that can demonstrate the bug. Turns out, the procedure being passed does not need to be fastcall; it being a procedure is sufficient.

#include <stdio.h>                                    

void inner () {}                                      

struct Thing {                                        
  void _fastcall outer (void (*formal)());            
};                                                    

void _fastcall Thing::outer (void (*formal)()) {      
  printf("this = %p, formal = %p\n", this, formal);   
}                                                     

void main () {                                        
  Thing thing;                                        
  printf("&thing = %p, inner = %p\n", &thing, inner); 
  thing.outer(inner);                                 
}                                  

Compiling it in small memory model, with 16-bit code pointers, triggers the bug, as depicted below. Compiling in compact model, where function pointers are 32-bit and don't fit into a single 16-bit register, does not. (Never mind that this printf template is not entirely correct for when data pointers and code pointers can have different sizes.)

#retrocomputing #borland #borlandcpp