From 3045519bd4fd9344ed475b793bc60f0d6fbf3e35 Mon Sep 17 00:00:00 2001
From: CrazyEttin <>
Date: Fri, 28 May 2021 00:53:34 +0300
Subject: [PATCH] Fix backspace not working at linebreak.

---
 src/os.asm | 68 +++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 50 insertions(+), 18 deletions(-)

diff --git a/src/os.asm b/src/os.asm
index e7cad54..0688e9d 100644
--- a/src/os.asm
+++ b/src/os.asm
@@ -3,6 +3,10 @@
 mov ax, 0x1000
 mov ds, ax
 
+mov ah, 0xf
+int 0x10
+mov byte [cpl], ah
+
 mov si, welcome
 call print
 
@@ -68,30 +72,33 @@ ret
 
 read:
 call clear
+mov bl, 0
+mov ah, 0x3
+int 0x10
+mov byte [.lastline], dh
 mov di, input
-mov cl, 0
 .loop:
 mov ah, 0
 int 0x16
+cmp al, 0
+je .loop
 cmp al, 0xd
 je .return
 cmp al, 0x8
 je .backspace
-cmp cl, 0x80
+cmp bl, 0x80
 je .loop
-cmp al, 0x20
-je .space
 cmp al, 0x9
 je .erase
-cmp al, 0
-je .loop
+cmp al, 0x20
+je .space
 .character:
 mov byte [di], 0
 mov ah, 0xe
 int 0x10
 stosb
-inc cl
-jmp .loop
+inc bl
+jmp .linecheck
 .erase:
 mov al, 0x20
 jmp .character
@@ -102,34 +109,57 @@ mov al, byte [di]
 mov ah, 0xe
 int 0x10
 inc di
-inc cl
+inc bl
+.linecheck:
+mov ah, 0x3
+int 0x10
+cmp dh, [.lastline]
+jle .loop
+mov byte [.lastline], dh
 jmp .loop
 .backspace:
-cmp cl, 0
+cmp bl, 0
 je .loop
+mov ah, 0x3
+int 0x10
+cmp dl, 1
+je .prevline
 mov ah, 0xe
 int 0x10
 dec di
-dec cl
+dec bl
+jmp .loop
+.prevline:
+mov ah, 0x2
+dec dh
+mov dl, [cpl]
+int 0x10
+dec di
+dec bl
 jmp .loop
 .return:
 mov di, input.end
-.tspfind:
+.findtrailingspace:
 dec di
 cmp byte [di], 0
-je .tspfind
+je .findtrailingspace
 cmp byte [di], 0x20
-je .tsperase
+je .erasetrailingspace
 jmp .done
-.tsperase:
+.erasetrailingspace:
 mov al, 0
 stosb
 dec di
-jmp .tspfind
+jmp .findtrailingspace
 .done:
+mov ah, 0x2
+mov dh, [.lastline]
+int 0x10
 mov si, newline
 call print
 ret
+.lastline:
+db 0
 
 compare:
 mov al, [si]
@@ -162,7 +192,6 @@ mov [di], bl
 inc di
 dec cx
 jnz .loop
-; mov si, input
 ret
 .hex:
 db "0123456789abcdef"
@@ -176,7 +205,7 @@ ret
 .input:
 db "Input:", 0xd, 0xa, "* Typing a character overwrites the cursor location.", 0xd, 0xa, "* The tab key erases the cursor location.", 0xd, 0xa, "* The space and backspace keys move the cursor.", 0xd, 0xa, 0
 .commands:
-db "Commands:", 0xd, 0xa, "* help: you are reading it.", 0xd, 0xa, "* hello: a hello world program.", 0xd, 0xa, "* echo: echoes its input.", 0xd, 0xa, "* keycode: echoes the BIOS scancode of a key.", 0xd, 0xa, 0
+db "Commands:", 0xd, 0xa, "* help: you are reading it.", 0xd, 0xa, "* hello: a hello world program.", 0xd, 0xa, "* echo: echoes its input.", 0xd, 0xa, "* keycode: echoes the BIOS code of a key.", 0xd, 0xa, 0
 
 hello:
 mov si, .msg
@@ -223,6 +252,9 @@ db 0
 
 ;Data
 
+cpl:
+db 0
+
 welcome:
 db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0xd, 0xa, 0