X-Git-Url: https://git.wirehaze.ovh/lifeboot.git/blobdiff_plain/a2d64c2f826170d6fd227f1f958ee75facabca4a..996bd9ab6f26e318e4b678f4b11d81bb8a8c5164:/lifeboot.asm diff --git a/lifeboot.asm b/lifeboot.asm index 7a70c62..8f11b87 100644 --- a/lifeboot.asm +++ b/lifeboot.asm @@ -1,77 +1,361 @@ bits 16 -org 0x7c00 +org 7c00h -%define ORG 0x7c00 ; where we are loaded initially +; ============================================================================= -%define VGA_SEG 0xb800 ; video memory starts at 0xb8000 -%define VGA_COL 80 -%define VGA_ROW 25 -%define VGA_LENW VGA_COL * VGA_ROW +; settings -------------------------------------------------------------------- -%define FILL_CHAR ' ' -%define PRINT_COLOR 0x07 ; grey on black +%define DEAD ' ' ; char to represent a dead cell +%define ALIVE '.' ; char to represent an alive cell +%define PRINT_COLOR 07h ; grey on black + +%define WAIT_DELAY_CX 01h ; cx:dx = delay in microseconds +%define WAIT_DELAY_DX 00h + +; constants ------------------------------------------------------------------- + +%define COLS 80 +%define ROWS 25 +%define VGAPGSZ 1000h + +; memory layout --------------------------------------------------------------- + +%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) + +; ============================================================================= ; entry point ----------------------------------------------------------------- ; initialize segment registers +mov ax, VGA >> 4 +mov es, ax + xor ax, ax mov ds, ax -mov es, ax mov ss, ax ; set stack pointers -mov sp, ORG mov bp, ORG +mov sp, bp -; clear screen ---------------------------------------------------------------- +; 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 ; video services -; clear video memory -mov cx, VGA_LENW -mov ax, VGA_SEG -mov es, ax -xor di, di -mov ax, (PRINT_COLOR << 8) | FILL_CHAR +; initialize xss + +set_xss_seed: + +mov ah, 00h ; get +int 1ah ; system time + +cmp dx, 0 +je set_xss_seed ; if seed is 0, xs wont work properly + +mov [xss], dx ; cx:dx = number of clock ticks since midnight + +; initialize currvgapg +mov word [currvgapg], 0 + +; start simulation from random state ------------------------------------------ + +start: + +call init_grid + +; apply game of life's rules to determine the next state ---------------------- + +next_state: + +call vsync_wait +call write_next_vga_page +call delay +call flip_vga_page + +jmp next_state + +; ============================================================================= + +; functions ------------------------------------------------------------------- + +; delay() - suspend program execution temporarily ----------------------------- + +; clobbers ah, cx, dx + +delay: + +mov cx, WAIT_DELAY_CX +mov dx, WAIT_DELAY_DX + +mov ah, 86h +int 15h ; wait + +ret + +; vsync_wait() - wait for display to enter the next VBlank cycle -------------- + +; clobbers ax, dx + +vsync_wait: + +mov dx, 3dah ; input status #1 register + +.wait_on: + in al, dx + test al, 08h ; vertical retrace bit + jnz .wait_on + +.wait_off: + in al, dx + test al, 08h + jz .wait_off + +ret + +; xs() - xorshift pseudorandom number generator ------------------------------- + +; output: +; [xss] = updated state + +; clobbers bx, dx + +xs: + +mov bx, [xss] +mov dx, bx + +shl dx, 1 ; dx = xss << 1 +xor bx, dx ; bx = xss ^ (xss << 1) +mov dx, bx + +shr dx, 3 ; dx = xss' >> 3 +xor bx, dx ; bx = xss' ^ (xss' >> 3) +mov dx, bx + +shl dx, 10 ; dx = xss'' << 10 +xor bx, dx ; bx = xss'' ^ (xss'' << 10) +mov [xss], bx + +ret + +; init_grid() - initialize grid cells randomly -------------------------------- + +; clobbers ax, bx, cx, dx, di + +init_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) + + test word [xss], 0b11 + + jnz .nz ; if ([xss] % 4 == 0) + mov al, ALIVE ; al = ALIVE + +.nz: + stosw ; [es:di] = ax ; di += 2 + + loop .write_cell ; } while (--cx) + +ret -rep stosw ; fill cx words at es:di with ax +; flip_vga_page() - flip active display page ---------------------------------- -; errors ---------------------------------------------------------------------- +; clobbers ax, dx -hello: -mov si, str.hello +flip_vga_page: -; print the error message string in si and halt -; note: we assume es = VGA_SEG and ds = 0 -printerr: -xor di, di -mov ah, PRINT_COLOR +call vsync_wait -; es:di = video memory -; ds:si = error message -; al = current char -; ah = color attribute +xor word [currvgapg], VGAPGSZ ; flip currvgapg +setnz al ; al = !(currvgapg == 0) -write_char: -lodsb ; al = [ds:si], si += 1 -or al, al ; on null terminator, -jz halt ; halt -stosw ; [es:di] = ax, di += 2 -jmp write_char +mov ah, 05h ; select active display page +int 10h ; video services + +ret + +; alive_neighbours() ---------------------------------------------------------- + +; 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] + jz .continue ; if (!i && !j) continue + + mov al, [bp - 1] + add al, [bp - 4] ; al = row + i + + cmp al, 0 + jl .continue ; if (row + i < 0) continue + + cmp al, ROWS + jge .continue ; if (row + i >= ROWS) continue + + mov ah, [bp - 2] + add ah, [bp - 5] ; ah = col + j + + cmp ah, 0 + jl .continue ; if (col + j < 0) continue + + cmp ah, COLS + jge .continue ; if (col + j >= COLS) 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) continue + jne .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 + +; 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 + +write_next_cell_state: + +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 + +; write_next_vga_page() ------------------------------------------------------- + +; clobbers di, si, ax, bx, cx, dx + +write_next_vga_page: + +mov si, [currvgapg] ; es:si -> current page + +mov di, VGAPGSZ +xor di, si ; es:di -> next page + +xor cx, cx ; i = 0 + +.update_loop: +call write_next_cell_state + +inc cx +cmp cx, COLS * ROWS +jl .update_loop ; for i in [0 .. COLS * ROWS - 1] + +ret + +; halt() - stop program execution --------------------------------------------- halt: -cli ; disable interrupts + +cli ; disable interrupts hlt jmp halt -; data ------------------------------------------------------------------------ - -str: -.hello: - db "lifeboot", 0 +; ============================================================================= times 510 - ($ - $$) db 0 ; fill remaining bytes with zeroes -dw 0xaa55 ; mbr magic byte +dw 0aa55h ; mbr magic byte