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

tmp_len = len6;

if (pos6 + tmp_len u> 64)
tmp_len = 64 - pos6;

if (unsigned_form)
GR[r1] = zero_ext(shift_right_unsigned(GR[r3], pos6), tmp_len);
else // signed_form
GR[r1] = sign_ext(shift_right_unsigned(GR[r3], pos6), tmp_len);

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