Is p_a_inv needed ?

[kagiannis]

Is p_a_inv needed ? It has many branches and maybe not so good precision.
p_inv is already fast.

Some platforms have hardware division that is faster than software division.
I think we can either make an inline function like this

inline PAL_DIV(float a,float b){
#ifdef HAVE_DIV
    return a/b;
#else
    /* compute inverse */
    union {
        float f;
        uint32_t x;
    } u = {b};
    /* First approximation */
    u.x = 0x7EEEEBB3 - u.x;
    /* Refine */
    u.f = u.f * (2 - u.f * cur);
    u.f = u.f * (2 - u.f * cur);
    u.f = u.f * (2 - u.f * cur);
    return a*u.f
#endif
}

and use it when division is needed
or use division in every case and let the compiler to do the division