X-Git-Url: https://git.wirehaze.ovh/lifeboot.git/blobdiff_plain/77ca36691072482fee62722117cd364912f2ffbf..refs/heads/main:/lifeboot.asm diff --git a/lifeboot.asm b/lifeboot.asm index 278bf32..739df40 100644 --- a/lifeboot.asm +++ b/lifeboot.asm @@ -1,66 +1,128 @@ bits 16 -org 0x7c00 +org 7c00h -%define ORG 0x7c00 -%define VGA 0xb8000 +; ============================================================================= + +; settings -------------------------------------------------------------------- + +%define DEAD ' ' ; char to represent a dead cell +%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 1000h ; (bytes) -%define DEAD ' ' ; char to represent a dead cell -%define ALIVE '#' ; char to represent an alive cell -%define PRINT_COLOR 0x07 ; grey on black +; memory layout --------------------------------------------------------------- + +%define ORG 7c00h +%define VGA 0b8000h +%define DAT ORG + 512 -%define GRID ORG + 512 ; current cell grid (80 * 25 bytes) -%define NEXT_GRID GRID + COLS * ROWS ; next cell grid (80 * 25 bytes) -%define XSS NEXT_GRID + COLS * ROWS ; xs() state +; 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 es, ax ; es:0 -> video memory + xor ax, ax -mov ds, ax -mov es, ax -mov ss, ax +mov ds, ax ; ds = 0 +mov ss, ax ; ss = 0 ; set stack pointers -mov sp, ORG mov bp, ORG +mov sp, bp ; clear direction flag cld ; disable cursor -mov ch, 0x3f -mov ah, 0x01 -int 0x10 +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 -; setup ----------------------------------------------------------------------- +mov [xss], dx -setup: +; initialize currvgapg +mov word [currvgapg], 0 + +; start simulation from random state ------------------------------------------ + +start: call init_grid -call print_grid +mov word [iter], 0 -jmp halt +.next_state: + + call vsync_wait + call update_grid + + call vsync_wait + call flip_vgapg + + inc word [iter] + cmp word [iter], ITER_LIM + jl .next_state + +jmp start ; reset + +; ============================================================================= ; functions ------------------------------------------------------------------- +; vsync_wait() - wait for display to enter the next retrace cycle ------------- + +; clobbers al, dx + +vsync_wait: + +mov dx, 3dah ; input status #1 register + +.wait_retrace_end: + in al, dx + test al, 08h ; vertical retrace bit + jnz .wait_retrace_end + +.wait_retrace_start: + in al, dx + test al, 08h + jz .wait_retrace_start + +ret + ; xs() - xorshift pseudorandom number generator ------------------------------- ; output: -; [XSS] = updated state +; [xss] = updated state +; bx = [xss] ; clobbers bx, dx xs: -mov bx, [XSS] +mov bx, [xss] mov dx, bx shl dx, 1 ; dx = xss << 1 @@ -73,65 +135,199 @@ mov dx, bx shl dx, 10 ; dx = xss'' << 10 xor bx, dx ; bx = xss'' ^ (xss'' << 10) -mov [XSS], bx +mov [xss], bx ret -; init_grid() - initialize GRID cells with random values ---------------------- - -; (*) expects es = 0. +; init_grid() - initialize grid cells randomly -------------------------------- ; clobbers ax, bx, cx, dx, di init_grid: -mov di, GRID ; es:di -> GRID +mov ah, PRINT_COLOR ; ah = color attribute +mov di, [currvgapg] ; es:di -> grid start mov cx, COLS * ROWS ; for each cell .write_cell: ; do { - call xs ; [XSS] = rand - mov al, DEAD ; al = DEAD (likely) + call xs ; bx = random value + mov al, DEAD ; al = DEAD - test [XSS], 0b11 + test bx, 0b11 - jnz .nz ; if ([XSS] % 4 == 0) + jnz .nz ; if (bx % 4 == 0) mov al, ALIVE ; al = ALIVE .nz: - stosb ; [es:(di++)] = al + stosw ; [es:di] = ax, di += 2 loop .write_cell ; } while (--cx) ret -; print_grid() - print GRID cells to screen ----------------------------------- +; flip_vgapg() - flip active display page ------------------------------------- -; (*) this function expects ds = 0 when called and sets es = 0 before -; returning. this is simpler because in the rest of the program we want the -; segment registers to be zeroed anyway. +; output: +; [currvgapg] ^= VGAPGSZ -; clobbers ax, cx, di, si +; clobbers ax -print_grid: +flip_vgapg: -mov ax, VGA >> 4 -xor di, di +xor word [currvgapg], VGAPGSZ -mov es, ax ; es:di -> VGA -mov si, GRID ; ds:si -> GRID +setnz al ; al = !(currvgapg == 0) +mov ah, 05h ; select active display page +int 10h ; bios video services -mov ah, PRINT_COLOR ; ah = color attribute +ret -mov cx, COLS * ROWS ; for each cell +; 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, ROWS ; if ((unsigned)(row + i) >= ROWS) + jae .continue ; continue + + mov ah, [bp - 2] + add ah, [bp - 5] ; ah = col + j + + cmp ah, COLS ; if ((unsigned)(col + j) >= COLS) + jae .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 + +shr ax, 1 +cmp ax, 1 ; if (n != 2 || n != 3) +jne .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 + +mov di, VGAPGSZ +xor di, si ; es:di -> next page + +mov cx, COLS * ROWS - 1 ; for each cell (index) -.print_cell: ; do { +.update_loop: ; do { - lodsb ; al = [ds:(si++)] - stosw ; [es:di] = ax ; di += 2 + call update_cell - loop .print_cell ; } while (--cx) + dec cx + jns .update_loop ; } while (--cx > 0) -mov es, cx ; es = 0 ret ; halt() - stop program execution --------------------------------------------- @@ -142,7 +338,7 @@ cli ; disable interrupts hlt jmp halt -; ----------------------------------------------------------------------------- +; ============================================================================= times 510 - ($ - $$) db 0 ; fill remaining bytes with zeroes -dw 0xaa55 ; mbr magic byte +dw 0aa55h ; mbr magic byte