X-Git-Url: https://git.wirehaze.ovh/lifeboot.git/blobdiff_plain/a66d954911e53705de79f2318a6e610e39d11889..a85b4d8ad6e3a6e4b22aaa13f14169db2495be16:/lifeboot.asm?ds=sidebyside

diff --git a/lifeboot.asm b/lifeboot.asm
index 07d9c5a..655febb 100644
--- a/lifeboot.asm
+++ b/lifeboot.asm
@@ -1,83 +1,147 @@
 bits 16
 org 0x7c00
 
-%define ORG 0x7c00
-%define VGA 0xb8000
+; =============================================================================
 
-%define COLS 80
-%define ROWS 25
+; 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
+
+; constants -------------------------------------------------------------------
+
+%define COLS 80
+%define ROWS 25
+%define VGAPGSZ (COLS * ROWS * 2 + 96)  ; why 96 ??????
 
-%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
+; memory layout ---------------------------------------------------------------
+
+%define ORG 0x7c00
+%define VGA 0xb8000
+%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 direction flag
 cld
 
 ; disable cursor
-mov ch, 0x3f
-mov ah, 0x01
-int 0x10
+mov ch, 0x3f                ; cursor start and options
+mov ah, 0x01                ; set text-mode cursor shape
+int 0x10                    ; video services
 
-; setup -----------------------------------------------------------------------
+; initialize xss
 
-setup:
+set_xss_seed:
 
-; initialize xss
 mov ah, 0x00                ; get
 int 0x1a                    ;  system time
-mov [XSS], dx               ; cx:dx = number of clock ticks since midnight
 
-; initialize grid
-mov di, GRID                ; es:di -> GRID
-mov cx, COLS * ROWS         ; for each cell
+cmp dx, 0
+je set_xss_seed             ; if seed is 0, xs wont work properly
 
-.initgrid:                  ; do {
-    call xs                 ;     [XSS] = rand
-    mov al, DEAD            ;     al = DEAD (likely)
+mov [xss], dx               ; cx:dx = number of clock ticks since midnight
 
-    test [XSS], 0b11
+; initialize currvgapg
+mov word [currvgapg], 0
 
-    jnz  .initgrid_nz       ;     if ([XSS] % 4 == 0)
-    mov al, ALIVE           ;         al = ALIVE
+; start simulation from random state ------------------------------------------
 
-.initgrid_nz:
-    stosb                   ;     [es:(di++)] = al
+start:
 
-    loop .initgrid          ; } while (--cx)
+call init_grid
 
-call print_grid
+; apply game of life's rules to determine the next state ----------------------
 
-jmp halt
+next_state:
+
+call vsync_wait
+call write_next_vga_page
+call wait_keypress
+call flip_vga_page
+
+jmp next_state
+
+; =============================================================================
 
 ; functions -------------------------------------------------------------------
 
+; delay() - suspend program execution temporarily -----------------------------
+
+; clobbers ah, cx, dx
+
+delay:
+
+mov cx, WAIT_DELAY          ; cx:dx = interval in microseconds
+mov dx, 0
+
+mov ah, 0x86
+int 0x15                    ; wait
+
+ret
+
+; wait_keypress() - wait for any keypress -------------------------------------
+
+; clobbers: ax
+
+wait_keypress:
+
+mov ah, 0x00        ; read key press
+int 0x16            ; keyboard services
+
+ret
+
+; vsync_wait() - wait for display to enter the next VBlank cycle --------------
+
+; clobbers ax, dx
+
+vsync_wait:
+
+mov dx, 0x3da               ; input status #1 register
+
+.wait_on:
+    in al, dx
+    test al, 0x08           ; vertical retrace bit
+    jnz .wait_on
+
+.wait_off:
+    in al, dx
+    test al, 0x08
+    jz .wait_off
+
+ret
+
 ; xs() - xorshift pseudorandom number generator -------------------------------
 
 ; output:
-; [XSS]     = updated state
+; [xss]     = updated state
 
 ; clobbers bx, dx
 
 xs:
 
-mov bx, [XSS]
+mov bx, [xss]
 mov dx, bx
 
 shl dx, 1                   ; dx = xss << 1
@@ -90,38 +154,206 @@ mov dx, bx
 
 shl dx, 10                  ; dx = xss'' << 10
 xor bx, dx                  ; bx = xss'' ^ (xss'' << 10)
-mov [XSS], bx
+mov [xss], bx
 
 ret
 
-; print_grid() - print GRID cells to screen -----------------------------------
+; init_grid() - initialize grid cells randomly --------------------------------
 
-; (*) 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.
+; clobbers ax, bx, cx, dx, di
 
-; clobbers ax, cx, di, si
+init_grid:
 
-print_grid:
+mov ah, PRINT_COLOR         ; ah = color attribute
+mov di, [currvgapg]         ; es:di -> grid start
+mov cx, COLS * ROWS         ; for each cell
 
-mov ax, VGA >> 4
-xor di, di
+.write_cell:                ; do {
+    call xs                 ;     [xss] = rand
+    mov al, DEAD            ;     al = DEAD (likely)
 
-mov es, ax                  ; es:di -> VGA
-mov si, GRID                ; ds:si -> GRID
+    test word [xss], 0b11
 
-mov ah, PRINT_COLOR         ; ah = color attribute
+    jnz  .nz                ;     if ([xss] % 4 == 0)
+    mov al, ALIVE           ;         al = ALIVE
 
-mov cx, COLS * ROWS         ; for each cell
+.nz:
+    stosw                   ;     [es:di] = ax ; di += 2
 
-.print_cell:                ; do {
+    loop .write_cell        ; } while (--cx)
 
-    lodsb                   ;     al = [ds:(si++)]
-    stosw                   ;     [es:di] = ax ; di += 2
+ret
+
+; flip_vga_page() - flip active display page ----------------------------------
+
+; clobbers ax, dx
+
+flip_vga_page:
+
+call vsync_wait
+
+xor word [currvgapg], VGAPGSZ   ; flip currvgapg
+setnz al                        ; al = !(currvgapg == 0)
+
+mov ah, 0x05                ; select active display page
+int 0x10                    ; 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
 
-    loop .print_cell        ; } while (--cx)
+inc cx
+cmp cx, COLS * ROWS
+jl .update_loop             ; for i in [0 .. COLS * ROWS - 1]
 
-mov es, cx                  ; es = 0
 ret
 
 ; halt() - stop program execution ---------------------------------------------
@@ -132,7 +364,7 @@ cli                         ; disable interrupts
 hlt
 jmp halt
 
-; -----------------------------------------------------------------------------
+; =============================================================================
 
 times 510 - ($ - $$) db 0   ; fill remaining bytes with zeroes
 dw 0xaa55                   ; mbr magic byte