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

if (imm_form) {
tmp_src = (merge_form ? sign_ext(imm1,1) : sign_ext(imm8, 8));
tmp_nat = merge_form ? GR[r3].nat : 0;
tmp_len = len6 ;
} else { // register_form
tmp_src = GR[r2];
tmp_nat = (merge_form ? GR[r3].nat : 0) || GR[r2].nat;
tmp_len = merge_form ? len4 : len6 ;
}
if (pos6 + tmp_len u> 64)
tmp_len = 64 - pos6;

if (merge_form)
GR[r1] = GR[r3];
else // zero_form
GR[r1] = 0;

GR[r1]{(pos6 + tmp_len - 1):pos6} = tmp_src{(tmp_len - 1):0};
GR[r1].nat = tmp_nat;
}