almost

[lifeboot.git] / lifeboot.asm

diff --git a/lifeboot.asm b/lifeboot.asm
index 6d95c7cfee143213269e43a3da317f1abff75698..658abe719824f5cc7a97dc2af2ec281ec469289c 100644 (file)
--- a/lifeboot.asm
+++ b/lifeboot.asm
@@ -191,12 +191,80 @@ ret
 ; output:
 ; ax = # alive neighbours
 
-; clobbers ?
+; clobbers ax, bx, dx
 
 alive_neighbours:
+enter 5, 0
 
-; todo
+; [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
+
+        test 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() -----------------------------------------------------
@@ -209,7 +277,7 @@ ret
 ; output:
 ; [es:di + cx * 2] = updated cell state
 
-; clobbers ?
+; clobbers ax, bx, dx
 
 write_next_cell_state:
 
@@ -221,7 +289,7 @@ shl bx, 1
 mov dx, [es:si + bx]        ; dl = cell current state
 
 test dl, ALIVE              ; if (ALIVE) {
-jne 1f
+jne .else
 
 test ax, 2                  ;     if (n < 2)
 jl .dead                    ;         return DEAD
@@ -231,7 +299,7 @@ jg .dead                    ;         return DEAD
 
 jmp .alive                  ;     return ALIVE
 
-1:                          ; }
+.else:                      ; }
 
 test ax, 3                  ; if (n != 3)
 jne .dead                   ;     return DEAD
@@ -250,7 +318,7 @@ ret
 
 ; write_next_vga_page() -------------------------------------------------------
 
-; clobbers di, si, cx
+; clobbers di, si, ax, bx, cx, dx
 
 write_next_vga_page: