Tag: software

Assembly Language Counting Program

I have been learning x86 assembly language. I know a little bit from years ago but now it is coming back to me. I formerly did 16 bit DOS hobby programs. This is 32 bit Linux programming in assembly using FASM as my assembler.

format ELF executable
entry main

main: ; the main function of our assembly function, just as if I were writing C.

; I can load any string address into eax and print it!

mov eax,msg
call putstring
mov eax,main_string ; move the address of main_string into eax register
call putstring


mov eax,0
loop1:
call putint
inc eax
cmp eax,16;
jnz loop1

mov eax, 1  ; invoke SYS_EXIT (kernel opcode 1)
mov ebx, 0  ; return 0 status on exit - 'No Errors'
int 80h

; this is where I keep my string variables

msg: db 'Hello World!', 0Ah,0     ; assign msg variable with your message string
main_string db 'This is the assembly counting program!',0Ah,0
int_string db 32 dup '?',0Ah,0

; this is where I keep my function definitions

putstring: ; function to print zero terminated string pointed to by register eax

mov edx,eax ; copy eax to edx as well. Now both registers have the address of the main_string

strlen_start: ; this loop finds the lenge of the string as part of the putstring function

cmp [edx],byte 0 ; compare byte at address edx with 0
jz strlen_end ; if comparison was zero, jump to loop end because we have found the length
inc edx
jmp strlen_start

strlen_end:
sub edx,eax ; edx will now have correct number of bytes when we use it for the system write call

mov ecx,eax ; copy eax to ecx which must contain address of string to write
mov eax, 4  ; invoke SYS_WRITE (kernel opcode 4)
mov ebx, 1  ; write to the STDOUT file
int 80h     ; system call to write the message

ret ; this is the end of the putstring function return to calling location

putint: ; function to output decimal form of whatever integer is in eax

push eax ;save eax on the stack to restore later

mov ebx,int_string+31 ;address of start digits

digits_start:

mov edx,0;
mov esi,10
div esi
add edx,'0'
mov [ebx],dl
cmp eax,0
jz digits_end
dec ebx
jmp digits_start

digits_end:

mov eax,ebx ; now that the digits have been written to the string, display it!
call putstring

pop eax  ;load eax from the stack so it will be as it was before this function was called
ret

; This Assembly source file has been formatted for the FASM assembler.
; The following 3 commands assemble, give executable permissions, and run the program
;
;	fasm main.asm
;	chmod +x main
;	./main

This program only works on computers with Intel x86 CPUs and running a Linux distribution. the “int 80h” instructions mean interrupt 128. For some reason, this calls the Linux kernel. I don’t know why it works this way but I do know enough assembly to write my own string and integer routines to replace printf since it is not available in pure assembly like I could in the C programming language.

September 28, 2025

3 SDL Examples

This post isn’t Chess related but it is still very nerdy. I have made 3 different SDL programs that all do the exact same thing. However they are written using different SDL versions over time as the API has changed. Therefore, SDL version 1,2, and 3 source code is provided as well as the commands to compile them!

SDL Version 1

#include <stdio.h>
#include <SDL.h>
int width=1280,height=720;
int loop=1;
SDL_Surface *surface;
SDL_Event e;
int main(int argc, char **argv)
{
 if(SDL_Init(SDL_INIT_EVERYTHING)){return 1;}

 SDL_putenv("SDL_VIDEO_WINDOW_POS=center");
 SDL_WM_SetCaption("SDL1 Program",NULL);
 surface=SDL_SetVideoMode(width,height,32,SDL_SWSURFACE);
 if(surface==NULL){return 1;}

 SDL_FillRect(surface,NULL,0xFF00FF);

 while(loop)
 {
  while(SDL_PollEvent(&e))
  {
   if(e.type==SDL_QUIT){loop=0;}
   if(e.type==SDL_KEYUP){if(e.key.keysym.sym==SDLK_ESCAPE){loop=0;}}
  }
  SDL_Flip(surface);
 }

 SDL_Quit();
 return 0;    
}

/*
SDL1 program that creates a window but nothing else.
Closes when user presses Esc or clicks the X of the window.
This is to test whether SDL1 programs can be compiled.

 With the sdl-config script:
 gcc -Wall -ansi -pedantic sdl1-test.c -o sdl1-test `sdl-config --cflags --libs` && ./sdl1-test

 Without the sdl-config script:
 gcc -Wall -ansi -pedantic sdl1-test.c -o sdl1-test -I/usr/include/SDL -D_GNU_SOURCE=1 -L/usr/lib/x86_64-linux-gnu -lSDL && ./sdl1-test
*/

SDL Version 2

#include <stdio.h>
#include <SDL.h>
int width=1280,height=720;
int loop=1;
SDL_Window *window;
SDL_Surface *surface;
SDL_Event e;
int main(int argc, char **argv)
{
 if(SDL_Init(SDL_INIT_VIDEO))
 {
  printf( "SDL could not initialize! SDL_Error: %s\n",SDL_GetError());return -1;
 }
 window=SDL_CreateWindow("SDL2 Program",SDL_WINDOWPOS_CENTERED,SDL_WINDOWPOS_CENTERED,width,height,SDL_WINDOW_SHOWN );
 if(window==NULL){printf( "Window could not be created! SDL_Error: %s\n", SDL_GetError() );return -1;}
 surface = SDL_GetWindowSurface( window ); /*get surface for this window*/
 SDL_FillRect(surface,NULL,0xFF00FF);
 SDL_UpdateWindowSurface(window);
 printf("SDL Program Compiled Correctly\n");
 while(loop)
 {
  while(SDL_PollEvent(&e))
  {
   if(e.type == SDL_QUIT){loop=0;}
   if(e.type == SDL_KEYUP)
   {
    if(e.key.keysym.sym==SDLK_ESCAPE){loop=0;}
   }
  }
 }
 SDL_DestroyWindow(window);
 SDL_Quit();
 return 0;
}

/*
 This source file is an example to be included in Chastity's Code Cookbook. This example follows the SDL version 2 which works differently than the most up to date version (version 3 at this time). There is also an updated version in the same repository that works with version 3.

 Linux Compile Command:

 With the sdl2-config script:
 gcc -Wall -ansi -pedantic sdl2-test.c -o sdl2-test `sdl2-config --cflags --libs` && ./sdl2-test

 Without the sdl2-config script:
 gcc -Wall -ansi -pedantic sdl2-test.c -o sdl2-test -I/usr/include/SDL2 -lSDL2 && ./sdl2-test
*/

SDL Version 3

#include <stdio.h>
#include <SDL.h>
int width=1280,height=720;
int loop=1;
SDL_Window *window;
SDL_Surface *surface;
SDL_Event e;
int main(int argc, char **argv)
{
 if(!SDL_Init(SDL_INIT_VIDEO))
 {
  printf( "SDL could not initialize! SDL_Error: %s\n",SDL_GetError());return -1;
 }
 window=SDL_CreateWindow("SDL3 Program",width,height,0);
 if(window==NULL){printf( "Window could not be created! SDL_Error: %s\n", SDL_GetError() );return -1;}
 surface = SDL_GetWindowSurface( window ); /*get surface for this window*/
 SDL_FillSurfaceRect(surface,NULL,0xFF00FF);
 SDL_UpdateWindowSurface(window);
 printf("SDL Program Compiled Correctly\n");
 while(loop)
 {
  while(SDL_PollEvent(&e))
  {
   if(e.type == SDL_EVENT_QUIT){loop=0;}
   if(e.type == SDL_EVENT_KEY_UP)
   {
    if(e.key.key==SDLK_ESCAPE){loop=0;}
   }
  }
 }
 SDL_DestroyWindow(window);
 SDL_Quit();
 return 0;
}

/*
 This source file is an example to be included in Chastity's Code Cookbook. By following the migration guide, I converted the SDL2-test program to the changes in SDL3.

 https://wiki.libsdl.org/SDL3/README-migration

 Windows Compile Command:

 gcc -Wall -ansi -pedantic sdl3-test.c -o sdl3-test -IC:/w64devkit/include/SDL3 -lSDL3 && sdl3-test

 Linux Compile Command:

 gcc -Wall -ansi -pedantic sdl3-test.c -o sdl3-test -I/usr/include/SDL3 -lSDL3 && ./sdl3-test

*/

No matter which of those I compile and run, I get the same result:

All the programs do is create a window and fill the whole thing with Magenta. It’s not that exciting, but it is pretty, and it shows that all 3 versions of SDL work on my Debian Linux machine.

August 19, 2025