.code
;;;randomizes or uses default seed
;;;if randomize not called, same sequence of randomness
;;;this just makes a 64bit seed
Randomize:
 .resv equ ebp-8
push ebp
mov ebp,esp
sub esp,8
  call [GetTickCount]
  xchg al,ah
  mov word[.resv],ax
  adc al,ah
  adc ah,al
  mov word[.resv+2],ax
  call [GetTickCount]
  neg ax
  mov word[.resv+4],ax
  sub ah,al
  adc al,ah
  mov word[.resv+6],ax
  movq mm0,qword[.resv]
  movq qword[seed],mm0
add esp,8
mov esp,ebp
pop ebp
retn 0

RandInt:
.resv equ ebp-8
.high equ ebp+8
push ebp
mov ebp,esp
sub esp,8
push edx
push ebx
xor edx,edx
  movq mm0, qword[seed]
  movq qword[.resv],mm0
  mov ecx,dword[.resv+4] ;;2nd half of seed
  mov eax,dword[.resv]   ;;1st half of seed
  shld eax,ecx,1         ;;shift in 1 bit from 2nd half to first
  mov dword[.resv],eax   ;;update seed in local memory
  adc ecx,0              ;;add the carry flag
  ror ecx,3              ;;odd roll-right
  bswap ecx              ;;make more random
  mov dword[.resv+4],ecx ;;update 2nd half of seed in local memory
  movq mm0, qword[.resv]
  movq qword[seed],mm0
  mov ecx,dword[.high]   ;;process high
  cmp ecx,-1
  je near .rdone         ;;if high = FFFFFFFFh retn rnd dword
  test ecx,ecx
  jz  near .rdone         ;;if high = 0 retn rnd dword
  inc ecx
  div ecx
  xchg eax,edx
.rdone:
pop ebx
pop edx
add esp,8
mov esp,ebp
pop ebp
retn 4

.data
;64bit seed default
seed db 0aah,011h,00h,0bbh,0ffh,22h,0ddh,77h
    

org 256

call set320x200x256
call initrandomz


mainloop:

mov ecx,320
call randomz3
mov bx,ax

mov ecx,200
call randomz3
mov cx,ax

push ecx
mov ecx,256
call randomz3
pop ecx

call putpixel320x200x256 ; al=color bx=x cx=y

push eax
call bkeycheck
cmp al,27
pop eax
jnz mainloop

call set80x25t

int 20h

initrandomz: ; modifies edx, eax
rdtsc
ret


randomz3: ; Z3 ecx=range transparent
push ebx  ; number returned is:  0 <= n < ecx
push edx
mov ebx,eax
rdtsc

mov dx,cx

mov cl,al
xor cl,ah
ror ch,4
xor bl,ch
and cx,$f
rol bx,cl
btc bx,cx
xor bx,ax
ror eax,16
xor bx,ax
ror eax,16
mov cl,al
xor cl,ah
ror ch,4
xor bl,ch
and cx,$f
ror bx,cl
btc bx,cx

mov cl,bl
.minorloop:
rol eax,cl
and cx,$f
btc ax,cx
loopw .minorloop
mov cl,bh
.majorloop:
ror eax,cl
and cl,$f
btc ax,cx
loopw .majorloop
mov cx,dx

mul ecx
mov eax,edx
pop edx
pop ebx
ret

putpixel320x200x256: ; al=color, bx=x, cx=y
        push    es
        push    $A000
        pop     es
        mov     di,cx   ; y
        shl     cx,2
        add     di,cx   ; 5y
        shl     di,6    ; 320y
        add     di,bx
        stosb
        pop     es
        ret

bkeycheck:  ;returns: AH = BIOS scan code AL = ASCII character note: enhanced
mov ah,0x11 ;Return: ZF set if no keystroke available, ZF clear if keystroke available
int 0x16    ;only checks buffer without removing key
ret

set320x200x256:
mov ax,$13
int $10
ret

set80x25t:
mov ax,$03
int $10
ret
    

$=0x0100
use16
;320*200*256
mov al, 0x13
int 0x10

;setup es
les cx, [bx]

;set grayscale
;xor ax, ax
;mov dx, 0x03c9
;setcolor:
;out dx, al
;out dx, al
;out dx, al
;inc ax
;jnz setcolor


next:
in al, 0x40
stosb
shl ax, 8
in al, 0x40
imul ax, 133
mov cx, ax
pausenow:
loop pausenow
mov ah, 1
int 0x16
jz next
ret