From 9065e2c59115466474d91727f29ae90938e01c1b Mon Sep 17 00:00:00 2001
From: CrazyEttin <>
Date: Sun, 6 Jun 2021 11:18:15 +0300
Subject: [PATCH] Protect registers from changes within calls and rename
 newline to printcrlf for the sake of consistency.

---
 source/byte2hexstr.inc |  6 ++++++
 source/cmpstr.inc      | 15 +++++++++++++--
 source/newline.inc     | 11 -----------
 source/printcrlf.inc   | 18 ++++++++++++++++++
 source/println.inc     |  4 ++--
 source/printstr.inc    | 12 +++++++++++-
 source/readln.inc      |  2 +-
 source/readstr.inc     |  7 +++++++
 source/system.asm      |  2 +-
 9 files changed, 59 insertions(+), 18 deletions(-)
 delete mode 100644 source/newline.inc
 create mode 100644 source/printcrlf.inc

diff --git a/source/byte2hexstr.inc b/source/byte2hexstr.inc
index df43b88..1dcdee3 100644
--- a/source/byte2hexstr.inc
+++ b/source/byte2hexstr.inc
@@ -2,6 +2,9 @@
 
 byte2hexstr:
 
+;Store the initial registers in the stack
+pusha
+
 ;Set a key for the hex digits
 mov si, .key
 
@@ -26,6 +29,9 @@ inc di
 dec cx
 jnz .loop
 
+;Load the initial registers from the stack
+popa
+
 ret
 
 .key:
diff --git a/source/cmpstr.inc b/source/cmpstr.inc
index 10597b0..5098175 100644
--- a/source/cmpstr.inc
+++ b/source/cmpstr.inc
@@ -2,6 +2,11 @@
 
 cmpstr:
 
+;Store the initial registers in the stack
+pusha
+
+.loop:
+
 ;Load characters
 mov al, [si]
 mov bl, [di]
@@ -19,14 +24,20 @@ je .eq
 ;Repeat
 inc si
 inc di
-jmp cmpstr
+jmp .loop
 
 .neq:
 ;Clear the carry flag
 clc
-ret
+jmp .done
 
 .eq:
 ;Set the carry flag
 stc
+
+.done:
+
+;Load the initial registers from the stack
+popa
+
 ret
\ No newline at end of file
diff --git a/source/newline.inc b/source/newline.inc
deleted file mode 100644
index 1dd912d..0000000
--- a/source/newline.inc
+++ /dev/null
@@ -1,11 +0,0 @@
-;Prints a newline
-
-newline:
-
-mov si, .newline
-call printstr
-
-ret
-
-.newline:
-db 0xd, 0xa, 0x0
diff --git a/source/printcrlf.inc b/source/printcrlf.inc
new file mode 100644
index 0000000..88814fd
--- /dev/null
+++ b/source/printcrlf.inc
@@ -0,0 +1,18 @@
+;Prints a newline
+
+printcrlf:
+
+;Store the initial registers in the stack
+pusha
+
+;Print the newline
+mov si, .crlf
+call printstr
+
+;Load the initial registers from the stack
+popa
+
+ret
+
+.crlf:
+db 0xd, 0xa, 0x0
diff --git a/source/println.inc b/source/println.inc
index 07e8509..86db73c 100644
--- a/source/println.inc
+++ b/source/println.inc
@@ -1,4 +1,4 @@
-;Prints a string from si until a null followed by a newline.
+;Prints a string from si until a null, followed by a newline.
 
 println:
 
@@ -6,6 +6,6 @@ println:
 call printstr
 
 ;Print a newline
-call newline
+call printcrlf
 
 ret
diff --git a/source/printstr.inc b/source/printstr.inc
index 71be922..4258d98 100644
--- a/source/printstr.inc
+++ b/source/printstr.inc
@@ -2,6 +2,11 @@
 
 printstr:
 
+;Store the initial registers in the stack
+pusha
+
+.loop:
+
 ;Load a character
 lodsb
 
@@ -11,10 +16,15 @@ je .done
 
 ;Print the character
 mov ah, 0xe
+mov bx, 0x0
 int 0x10
 
 ;Repeat
-jmp printstr
+jmp .loop
 
 .done:
+
+;Load the initial registers from the stack
+popa
+
 ret
diff --git a/source/readln.inc b/source/readln.inc
index d45d1e4..451b380 100644
--- a/source/readln.inc
+++ b/source/readln.inc
@@ -6,6 +6,6 @@ readln:
 call readstr
 
 ;Print a newline
-call newline
+call printcrlf
 
 ret
diff --git a/source/readstr.inc b/source/readstr.inc
index e9119ae..7422def 100644
--- a/source/readstr.inc
+++ b/source/readstr.inc
@@ -2,6 +2,9 @@
 
 readstr:
 
+;Store the initial registers in the stack
+pusha
+
 ;Store the input length in the stack
 mov ah, 0
 push ax
@@ -117,6 +120,10 @@ inc bl
 jmp .findend
 
 .done:
+
+;Load the initial registers from the stack
+popa
+
 ret
 
 .nextchar:
diff --git a/source/system.asm b/source/system.asm
index 3c3e49c..9feec80 100644
--- a/source/system.asm
+++ b/source/system.asm
@@ -2,11 +2,11 @@
 jmp start
 
 ;Calls
+%include "printcrlf.inc"
 %include "printstr.inc"
 %include "println.inc"
 %include "readstr.inc"
 %include "readln.inc"
-%include "newline.inc"
 %include "cmpstr.inc"
 %include "byte2hexstr.inc"