Protect registers from changes within calls and rename newline to printcrlf for the sake of consistency.

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:

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

source/newline.inc

@@ -1,11 +0,0 @@
-;Prints a newline
-
-newline:
-
-mov si, .newline
-call printstr
-
-ret
-
-.newline:
-db 0xd, 0xa, 0x0

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

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

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

source/readln.inc

@@ -6,6 +6,6 @@ readln:
 call readstr
 
 ;Print a newline
-call newline
+call printcrlf
 
 ret

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:

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"