Unify the x/y handling in the mouse handler a bit more

ponydos.asm

@@ -390,11 +390,15 @@ Y_MAX_VALUE equ 4*ROWS-1
 ;  bx = status
 ;  cl = negative bit # in ah
 ;  dx = MAX_VALUE
+;  zf = tested against overflow
 ; out
 ;  [mouse_x]/[mouse_y] updated appropriately
 ;  si = updated [mouse_x]/[mouse_y]
+;  di = di + 2
 ;  clobbers ax
 xy_handler:
+	jnz .overflow_return
+
 	; X and Y coördinates are stored as 9-bit signed integers
 	; using two's complement notation. The high bits are called
 	; "X negative" and "Y negative".
@@ -421,6 +425,10 @@ xy_handler:
 	.not_overflow:
 
 	mov [cs:di], si
+	
+	.overflow_return:
+	inc di
+	inc di
 	ret
 
 mouse_handler:
@@ -430,32 +438,28 @@ mouse_handler:
 
 	mov bx, [bp+2*8+10] ; status
 
-	xor si, si
-	mov di, mouse_x
-	mov dx, X_MAX_VALUE
-
-	test bl, X_OVERFLOW
-	jnz .x_end
 	.x:
+		xor si, si
+		mov di, mouse_x
+		mov dx, X_MAX_VALUE
 		mov ax, [bp+2*8+8]
 		mov cl, 3
-		call xy_handler
-	.x_end:
-	inc di
-	inc di ; mouse_y
 
-	test bl, Y_OVERFLOW
-	jnz .y_end
+		test bl, X_OVERFLOW
+		call xy_handler
+
 	.y:
 		inc si ; will be non-zero
 		mov ax, [bp+2*8+6]
 		mov cl, 2
 		;mov dx
 		mov dl, Y_MAX_VALUE
+
+		test bl, Y_OVERFLOW
 		call xy_handler
-	.y_end:
+
 	and bl, BUTTONS
-	mov [cs:di - mouse_y + mouse_buttons], bl
+	mov [cs:di], bl
 
 	popa
 	retf
@@ -482,7 +486,7 @@ resb 8 ; Rest of the memory allocation map
 
 mouse_x resw 1
 mouse_y resw 1 ; mouse_x + 2, do not touch
-mouse_buttons resb 1
+mouse_buttons resb 1 ; mouse_y + 2
 
 mouse_column resb 1
 mouse_row resb 1 ; mouse_column + 1