I am using assembly 8086emu and I need a numbers generator for 8 numbers. I tried to use this piece of code by @johnfound:
RANDGEN: ; generate a rand no using the system time
RANDSTART:
MOV AH, 00h ; interrupts to get system time
INT 1AH ; CX:DX now hold number of clock ticks since midnight
mov ax, dx
xor dx, dx
mov cx, 10
div cx ; here dx contains the remainder of the division - from 0 to 9
add dl, '0' ; to ascii from '0' to '9'
mov ah, 2h ; call interrupt to display a value in DL
int 21h
RET
but it is useful only when you generate 1 number.
I've tried to create pseudo-random function but I am pretty new to assembly and I did not succeed.
I would like to know if there is a way to translate java's Math.random()
function or something simular in assembly 8086.
Thanks
One simple pseudo random number generator multiplies the current number by 25173, then adds 13849 to it. This value now becomes the new random number.
If you started from the system timer like you did (this is called seeding the random number generator), this series of numbers will be random enough for simple tasks!
MOV AH, 00h ; interrupt to get system timer in CX:DX
INT 1AH
mov [PRN], dx
call CalcNew ; -> AX is a random number
xor dx, dx
mov cx, 10
div cx ; here dx contains the remainder - from 0 to 9
add dl, '0' ; to ascii from '0' to '9'
mov ah, 02h ; call interrupt to display a value in DL
int 21h
call CalcNew ; -> AX is another random number
...
ret
; ----------------
; inputs: none (modifies PRN seed variable)
; clobbers: DX. returns: AX = next random number
CalcNew:
mov ax, 25173 ; LCG Multiplier
mul word ptr [PRN] ; DX:AX = LCG multiplier * seed
add ax, 13849 ; Add LCG increment value
; Modulo 65536, AX = (multiplier*seed+increment) mod 65536
mov [PRN], ax ; Update seed = return value
ret
This implements a Linear Congruential Generator (LCG) with a power-of-2 modulus. %65536
happens for free because the low 16 bits of the product + increment are in AX, and the higher bits aren't.