How to pack small type to big type without memory load/store ?

[Jojo R]

Hi,

Form My ABI, float register is used by function call,
I want to pack float a and b into double v without any memory load/store,

The flowing is my demo:

Typedef union {
        float ff[2];
        double v;
} double_u;

Double pack_float (float a, float b) {

        double_u tmp;

        tmp.ff[0] = a;
        tmp.ff[1] = b;

        return tmp.v;
}

There is memory store in these statement:

tmp.ff[0] = a;
tmp.ff[1] = b;

Could someone give me some hints to avoid memory load/store ?

Jojo