sub Operation Font Conventions
if (PR[qp]) {
check_target_register;

tmp_src = (register_form ? GR[r2] : sign_ext(imm8, 8));
tmp_nat = (register_form ? GR[r2].nat : 0);

if (minus1_form)
GR[r1] = tmp_src - GR[r3] - 1;
else
GR[r1] = tmp_src - GR[r3];

GR[r1].nat = tmp_nat || GR[r3].nat;
}