So without optimization, it doesn't look good...

part 1 ;sign extend for c3 bpl .1 lda #$ff .byt $24;thanks optimizing tricks thread .1 lda #0;8/11 adc c3 sta c3

anc #$80 ;copy bit 7 to carry and A = A & $80 bcc + ;A is zero on plus, all fine sbc #$81 ;subtract $81 from $80 = $ff + ;carry always clear as a free gift