clone53421's Journal: Lagged Fibonacci Generator (80x86)

This program implements a lagged Fibonacci generator with constants j=7, k=10. A linear congruential generator is used to seed the list of initial values; the system timer is used to seed the LCG.

Initially I included a routine to print each random number so I could redirect the output into a .csv file and plot the points in Excel, but I've taken that code out. Now, the program instead switches to display mode 12 (640x480x16 graphics mode) and plots "snow" on the screen in random locations and colours. Pressing any key ends the program.

Like the other ones, paste this in Notepad and save it as a .bat file. Run it and it does the rest.

@echo off
goto batch
 
a
;Generates random numbers using an Additive Lagged Fibonacci Generator, j=7, k=10.
;The system timer (clock ticks since midnight) is used to seed a LCG to generate initial values
call 017d ;_seed
mov ax,0012
int 10 ;Set video mode 12 (640x480x16 graphics)
;_loop
call 014d ;_rand
mov bx,0005
xor dx,dx
div bx
shl ax,1
mov bx,0029
xor dx,dx
div bx
mov cx,ax ;CX holds the column number
call 014d ;_rand
mov bx,000c
xor dx,dx
div bx
mov bx,0005
mul bx
mov bx,0039
xor dx,dx
div bx
xchg ax,dx ;DX holds the row number
mov ah,0c
and al,0f
int 10 ;plot the pixel
;Check for keypress to exit
mov ah,06
mov dl,ff
int 21
jz 0108 ;_loop
mov ax,0002
int 10 ;Set video mode 2 (25x80x16 text)
mov ax,4c01
int 21 ;return to DOS
;Return the next random number in AX.
;_rand
xor bh,bh
mov bl,[01a2+14] ;_lastValues
mov ax,[bx+01a2] ;_lastValues
add bx,06
cmp bx,14
jl 0162 ;_next1rand
sub bx,14
;_next1rand
add ax,[bx+01a2] ;_lastValues
;Store the new random number (AX) in the last values history
mov bl,[01a2+14] ;_lastValues
mov [bx+01a2],ax ;_lastValues
;Increment our pointer to the oldest last value
inc bx
inc bx
cmp bx,14
jl 0178 ;_next2rand
sub bx,14
;_next2rand
mov [01a2+14],bl ;_lastValues
ret
;Seed the random number generator using the system timer
;_seed
xor ah,ah
int 1a ;Get ticks since midnight in CX:DX
mov [01a2],dx ;_lastValues
mov ax,dx
xor bx,bx
;_LCG
mov dx,4e35
mul dx
inc ax
inc bx
inc bx
mov [bx+01a2],ax ;_lastValues
cmp bx,12
jl 0189 ;_LCG
or ax,0001 ;LFG needs at least 1 odd initial value
mov [bx+01a2],ax ;_lastValues
ret
;_lastValues
dw 0,0,0,0,0,0,0,0,0,0
db 0
;_ASCIIZ
        db "lfg_snow.com",0
;_compile
        MOV AX,CS
        MOV DS,AX
        MOV AH,3C
        XOR CX,CX
        MOV DX,01b7 ;_ASCIIZ
        INT 21
        MOV BX,AX
        MOV CX,01b7 ;_ASCIIZ
        MOV DX,0100 ; where the program starts
        SUB CX,DX
        MOV AH,40
        INT 21
        MOV AH,3E
        INT 21
        MOV AX,4C00
        INT 21
 
r ip
1c4
g
q
 
:batch
if exist %0 goto extension
debug < %0.bat
goto run
 
:extension
debug < %0
 
:run
pause
cls
lfg_snow.com