Printing a string in NASM Win16 Assembly

Question

A small script that simply prints a given string. It's an improved snippet that combines some recommendations given in my post on string helper functions.

org 100h
mov si, hello
call puts
ret
puts:
 jmp .run
.putc:
 mov ah, 0Eh
 mov bx, 7
 int 10h
.run:
 lodsb
 cmp al, 0
 jne .putc
 ret
hello db "Hello World!", 0

Answer 1

You have all the elements. The only thing that can be eliminated is jmp .run, as follows:

org 0x100
 mov si, Prompt
 call puts
 ret
 puts: mov ah, 0xe
 mov bx, 7
 .read: lodsb
 or al, al
 jnz .post 
 ret
 .post: int 0x10
 jmp .read
 Prompt: db 'Hello World', 0

As INT 10H does not trash AH or BX, there is no need to reinitialize them each time through the loop.

• Cody Gray: Use TEST reg, reg to check for zero in preference to OR reg, reg, since the former is more likely to fuse with the conditional branch. I also find it more readable.
• Shift_Left: @CodyGray I agree, as test is more representative of what is being done and I think that's what you mean by more readable. Whereas or implies AL is being modified for some other reason.
• T145: I interpret "trashing" as having a value reset to some default value. Would this be accurate? If so, Is there a way to efficiently determine if an interrupt trashes a register? I've been using HelpPC as a reference for interrupts, and there's no mention of trashing.
• Shift_Left: I use trashing in the context that a register has been modified by an interrupt, function or subroutine where its value upon return is indeterminate. As to the reference your using, I think it would be safe to say that if nothing is returned, then nothing is modified either or it specifically states returned values.