bits 16
-org 0x7c00
+org 7c00h
; =============================================================================
; settings --------------------------------------------------------------------
%define DEAD ' ' ; char to represent a dead cell
-%define ALIVE '#' ; char to represent an alive cell
-%define PRINT_COLOR 0x07 ; grey on black
-%define WAIT_DELAY 0x02 ; 0.131072 seconds
+%define ALIVE '.' ; char to represent an alive cell
+%define PRINT_COLOR 07h ; grey on black
+%define ITER_LIM 500 ; reset the simulation after this # iterations
; constants -------------------------------------------------------------------
%define COLS 80
%define ROWS 25
-%define VGAPGSZ (COLS * ROWS * 2)
+%define VGAPGSZ 1000h ; (bytes)
; memory layout ---------------------------------------------------------------
-%define ORG 0x7c00
-%define VGA 0xb8000
+%define ORG 7c00h
+%define VGA 0b8000h
%define DAT ORG + 512
; static variables ------------------------------------------------------------
%define xss DAT ; xs() state (word)
%define currvgapg DAT + 2 ; current vga page near pointer (word)
+%define iter DAT + 4 ; current iteration # (word)
; =============================================================================
; entry point -----------------------------------------------------------------
+entry:
+
; initialize segment registers
mov ax, VGA >> 4
-mov ds, ax
-mov es, ax
+mov es, ax ; es:0 -> video memory
xor ax, ax
-mov ss, ax
+mov ds, ax ; ds = 0
+mov ss, ax ; ss = 0
; set stack pointers
mov bp, ORG
cld
; disable cursor
-mov ch, 0x3f ; cursor start and options
-mov ah, 0x01 ; set text-mode cursor shape
-int 0x10 ; video services
+mov ch, 3fh ; cursor start and options
+mov ah, 01h ; set text-mode cursor shape
+int 10h ; bios video services
; initialize xss
-mov ah, 0x00 ; get
-int 0x1a ; system time
-mov [xss], dx ; cx:dx = number of clock ticks since midnight
+.set_xss:
+ mov ah, 00h ; get system time
+ int 1ah ; bios time services
+ ; cx:dx = # clock ticks since midnight
+ or dx, dx
+ jz .set_xss ; wait for something meaningful
+
+mov [xss], dx
; initialize currvgapg
-mov word [currvgapg], VGAPGSZ
+mov word [currvgapg], 0
-; setup -----------------------------------------------------------------------
+; start simulation from random state ------------------------------------------
-setup:
+start:
call init_grid
-call flip_vga_page
-call delay
+mov word [iter], 0
-jmp setup
+.next_state:
-; =============================================================================
-
-; functions -------------------------------------------------------------------
+ call vsync_wait
+ call update_grid
-; delay() - suspend program execution temporarily -----------------------------
+ call vsync_wait
+ call flip_vgapg
-; clobbers ah, cx, dx
+ inc word [iter]
+ cmp word [iter], ITER_LIM
+ jl .next_state
-delay:
+jmp start ; reset
-mov cx, WAIT_DELAY ; cx:dx = interval in microseconds
-mov dx, 0
-
-mov ah, 0x86
-int 0x15 ; wait
+; =============================================================================
-ret
+; functions -------------------------------------------------------------------
-; vsync_wait() - wait for display to enter the next VBlank cycle --------------
+; vsync_wait() - wait for display to enter the next retrace cycle -------------
-; clobbers ax, dx
+; clobbers al, dx
vsync_wait:
-mov dx, 0x3da ; input status #1 register
+mov dx, 3dah ; input status #1 register
-.wait_on:
+.wait_retrace_end:
in al, dx
- test al, 0x08 ; vertical retrace bit
- jnz .wait_on
+ test al, 08h ; vertical retrace bit
+ jnz .wait_retrace_end
-.wait_off:
+.wait_retrace_start:
in al, dx
- test al, 0x08
- jz .wait_off
+ test al, 08h
+ jz .wait_retrace_start
ret
; output:
; [xss] = updated state
+; bx = [xss]
; clobbers bx, dx
mov cx, COLS * ROWS ; for each cell
.write_cell: ; do {
- call xs ; [xss] = rand
+ call xs ; bx = random value
mov al, DEAD ; al = DEAD (likely)
- test word [xss], 0b11
+ test bx, 0b11
- jnz .nz ; if ([xss] % 4 == 0)
+ jnz .nz ; if (bx % 4 == 0)
mov al, ALIVE ; al = ALIVE
.nz:
- stosw ; [es:di] = ax ; di += 2
+ stosw ; [es:di] = ax, di += 2
loop .write_cell ; } while (--cx)
ret
-; flip_vga_page() - flip active display page ----------------------------------
+; flip_vgapg() - flip active display page -------------------------------------
+
+; output:
+; [currvgapg] ^= VGAPGSZ
+
+; clobbers ax
+
+flip_vgapg:
+
+xor word [currvgapg], VGAPGSZ
+
+setnz al ; al = !(currvgapg == 0)
+mov ah, 05h ; select active display page
+int 10h ; bios video services
+
+ret
+
+; alive_neighbours() - get number of alive adjacent cells ---------------------
+
+; input:
+; es:si -> current grid
+; cx -> cell index
+
+; output:
+; ax = # alive neighbours
+
+; clobbers ax, bx, dx
+
+alive_neighbours:
+enter 5, 0
+
+; [bp - 1]: row
+; [bp - 2]: col
+; [bp - 3]: neighbours
+; [bp - 4]: i
+; [bp - 5]: j
+
+mov ax, cx ; ax = idx
+mov bl, COLS ; bl = COLS
+div bl ; al = idx / COLS, ah = idx % COLS
+
+mov [bp - 1], al ; row = idx / COLS
+mov [bp - 2], ah ; row = idx % COLS
+mov byte [bp - 3], 0 ; neighbours = 0
+
+mov byte [bp - 4], -1 ; i = -1
+.i: ; do {
+
+ mov byte [bp - 5], -1 ; j = -1
+.j: ; do {
+
+ mov al, [bp - 4]
+ or al, [bp - 5] ; if (!i && !j)
+ jz .continue ; continue
+
+ mov al, [bp - 1]
+ add al, [bp - 4] ; al = row + i
+
+ cmp al, 0 ; if (row + i < 0)
+ jl .continue ; continue
+
+ cmp al, ROWS ; if (row + i >= ROWS)
+ jge .continue ; continue
+
+ mov ah, [bp - 2]
+ add ah, [bp - 5] ; ah = col + j
+
+ cmp ah, 0 ; if (col + j < 0)
+ jl .continue ; continue
+
+ cmp ah, COLS ; if (col + j >= COLS)
+ jge .continue ; continue
+
+ movzx bx, ah ; bx = col + j
+
+ mov ah, COLS
+ mul ah ; ax = (row + i) * COLS
+
+ add bx, ax ; bx = cell index
+ shl bx, 1 ; bx = grid offset
+
+ mov dx, [es:si + bx] ; dl = cell state
+
+ cmp dl, ALIVE ; if (!ALIVE)
+ jne .continue ; continue
+
+ inc byte [bp - 3] ; neighbours++
+
+.continue:
+ inc byte [bp - 5]
+ cmp byte [bp - 5], 1
+ jle .j ; } while (++j <= 1)
+
+ inc byte [bp - 4]
+ cmp byte [bp - 4], 1
+ jle .i ; } while (++i <= 1)
+
+movzx ax, byte [bp - 3] ; ax = # alive neighbours
+
+leave
+ret
+
+; update_cell() - write next cell state ---------------------------------------
+
+; input:
+; es:si -> current grid
+; es:di -> next grid
+; cx -> cell index
+
+; output:
+; [es:di + cx * 2] = updated cell state
+
+; clobbers ax, bx, dx
+
+update_cell:
+
+call alive_neighbours ; ax = # alive neighbours
+
+mov bx, cx
+shl bx, 1
+
+mov dx, [es:si + bx] ; dl = cell current state
+
+cmp dl, ALIVE ; if (ALIVE) {
+jne .else
+
+cmp ax, 2 ; if (n < 2)
+jl .dead ; return DEAD
+
+cmp ax, 3 ; if (n > 3)
+jg .dead ; return DEAD
+
+jmp .alive ; return ALIVE
+
+.else: ; }
+
+cmp ax, 3 ; if (n != 3)
+jne .dead ; return DEAD
+
+.alive: ; return ALIVE
+mov dl, ALIVE
+jmp .write
+
+.dead:
+mov dl, DEAD
+
+.write:
+mov [es:di + bx], dx
+
+ret
+
+; update_grid() - write next grid (inactive vga page) -------------------------
+
+; clobbers di, si, ax, bx, cx, dx
+
+update_grid:
+
+mov si, [currvgapg] ; es:si -> current page
-; clobbers ax, dx
+mov di, VGAPGSZ
+xor di, si ; es:di -> next page
-flip_vga_page:
+mov cx, COLS * ROWS - 1 ; for each cell (index)
-call vsync_wait
+.update_loop: ; do {
-xor word [currvgapg], VGAPGSZ ; flip currvgapg
-setnz al ; al = !(currvgapg == 0)
+ call update_cell
-mov ah, 0x05 ; select active display page
-int 0x10 ; video services
+ dec cx
+ jns .update_loop ; } while (--cx > 0)
ret
; =============================================================================
times 510 - ($ - $$) db 0 ; fill remaining bytes with zeroes
-dw 0xaa55 ; mbr magic byte
+dw 0aa55h ; mbr magic byte
projects / lifeboot.git / blobdiff