[Thomas_Lord]

Slightly off topic. The article doesn't call it out but there's a lovely assembly hack here. In:

bec 1f / branch if no error

   jsr r5,error / error in file name

       <Input not found\n\0>; .even

   sys exit

jsr calls a subroutine passing the return address in register 5. The routine error interprets the return address as a pointer to the string.

r5 is incremented in a loop, outputing one character at a time. When the null is found, it's time to return.

The instructions used to return from "error:" aren't shown but there is a subtlety here, I think.

".even" after the string constant assures that the next instruction, "sys exit", to which "error:" is supposed to return, is aligned on an even address.

By implication, the return sequence in "error:" just be sure to increment r5, if r5 is odd. I am guessing something like the pseudo-code:

inc r5

and r5, fffe

ret r5

[ksherlock]

Yep!

http://minnie.tuhs.org/cgi-bin/utree.pl?file=V1/sh.s

    error:
        ...
	inc	r5 / inc r5 to point to return
	bic	$1,r5 / make it even

[Thomas_Lord]

Thanks! Nifty!