ASM: INVERT$ ( addr len -- addr len )
    *sp r1 mov,                    \ len to r1
    2 sp () r0 mov,                \ addr to r0
    r2 clr,
    begin,
        r0 ** r2 movb,              \ get a character in r2
        r2 $8000 ci,                \ compare to inverted space
        he if,
            r2 char z 96 + 256 * ci, \ compare to inverted z
            le if,
                r2 -$6000 ai,       \ convert to non-inverted character
                r2 r0 ** movb,      \ write the character back
            endif,
        else,
            r2 bl 256 * ci,             \ compare to space
            he if,
                r2 char z 256 * ci,     \ compare to z
                le if,
                    r2 $6000 ai,        \ convert to inverted character
                    r2 r0 ** movb,      \ write the character back
                endif,
            endif,
        endif,
        r0 inc,                     \ next address
        r1 dec,                     \ decrement len
    eq until,                       \ repeat if len>0
;ASM

: all cr 256 0 do i emit loop ;
: test s" THIS IS A TEST! this is a test 0123" ;
: ? test invert$ type ;


CODE: INVERT$                                                  
C054 C024 0002 04C2 D090 0282 8000 1A07 0282 DA00 1B03 0222    
A000 D402 1009 0282 2000 1A06 0282 7A00 1B03 0222 6000 D402    
0580 0601 16E9 ;CODE