From d675597120f4ebe3529e8bbc6ece0436031f0188 Mon Sep 17 00:00:00 2001
From: shikhin <draumr.shikhin@gmail.com>
Date: Sun, 19 Mar 2023 18:22:10 +0530
Subject: [PATCH] Combine x and y handling in mouse_handler

---
 ponydos.asm | 106 ++++++++++++++++++++++++++++------------------------
 1 file changed, 58 insertions(+), 48 deletions(-)

diff --git a/ponydos.asm b/ponydos.asm
index f3388d8..5e418e3 100644
--- a/ponydos.asm
+++ b/ponydos.asm
@@ -374,6 +374,48 @@ BUTTONS equ 0x03
 X_MAX_VALUE equ 2*COLUMNS-1
 Y_MAX_VALUE equ 4*ROWS-1
 
+; in:
+;  si = non-zero for Y
+;  di = &mouse_x/&mouse_y
+;  ax = X/Y
+;  bx = status
+;  cl = negative bit # in ah
+;  dx = MAX_VALUE
+; out
+;  mouse_x/mouse_y updated appropriately
+;  si = updated [mouse_x]/[mouse_y]
+;  di = di + 1
+;  clobbers ah
+xy_handler:
+	; 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".
+	mov ah, bl
+	shl ah, cl ; Shift negative bit to sign position
+	sar ah, 7 ; Fill entire byte with sign bit's value
+
+	test si, si
+	jz .not_y
+	neg ax
+
+	.not_y:
+	mov si, [cs:di]
+	add si, ax
+
+	;cmp si, 0
+	jge .not_underflow
+	xor si, si
+	.not_underflow:
+
+	cmp si, dx
+	jle .not_overflow
+	mov si, dx
+	.not_overflow:
+
+	mov [cs:di], si
+	inc di
+	ret
+
 mouse_handler:
 	pusha
 
@@ -384,61 +426,29 @@ mouse_handler:
 	test bl, X_OVERFLOW
 	jnz .x_end
 	.x:
-		mov si, [cs:mouse_x]
 
-		mov ax, [bp+2*8+8] ; X
-
-		; 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".
-		mov ah, bl
-		shl ah, 3 ; X negative is bit 4, shift it to sign position
-		sar ah, 7 ; Fill entire byte with sign bit's value
-
-		add si, ax
-
-		;cmp si, 0
-		jge .not_x_underflow
-		xor si, si
-		.not_x_underflow:
-
-		cmp si, X_MAX_VALUE
-		jle .not_x_overflow
-		mov si, X_MAX_VALUE
-		.not_x_overflow:
-
-		mov [cs:mouse_x], si
 	.x_end:
+		xor si, si
+		mov di, mouse_x
+		mov ax, [bp+2*8+8]
+		mov cl, 3
+		mov dx, X_MAX_VALUE
+		call xy_handler
 
 	test bl, Y_OVERFLOW
 	jnz .y_end
 	.y:
-		mov si, [cs:mouse_y]
-
-		mov ax, [bp+2*8+6] ; Y
-
-		mov ah, bl
-		shl ah, 2 ; Y negative is bit 5
-		sar ah, 7
-
-		; Y direction is flipped compared to our coöridinate space
-		sub si, ax
-
-		;cmp si, 0
-		jge .not_y_underflow
-		xor si, si
-		.not_y_underflow:
-
-		cmp si, Y_MAX_VALUE
-		jl .not_y_overflow
-		mov si, Y_MAX_VALUE
-		.not_y_overflow:
-
-		mov [cs:mouse_y], si
+		inc si ; won't be zero
+		inc di ; mouse_y
+		mov ax, [bp+2*8+6]
+		mov cl, 2
+		;mov dx
+		mov dl, Y_MAX_VALUE
+		call xy_handler
 	.y_end:
 
 	and bl, BUTTONS
-	mov [cs:mouse_buttons], bl
+	mov [cs:di], bl ; mouse_buttons
 
 	popa
 	retf
@@ -462,8 +472,8 @@ section .bss
 _bss_start:
 
 mouse_x resw 1
-mouse_y resw 1
-mouse_buttons resb 1
+mouse_y resw 1 ; mouse_x + 2
+mouse_buttons resb 1 ; mouse_y + 1
 
 mouse_column resb 1
 mouse_row resb 1