Description
In FTEQW, looking at the implementations of PF_normalize and PF_vlen, it seems like the following property is true:
normalize(v) == v * (1.0 / vlen(v))
using the MUL_VF and DIV_F instructions.
Non compiler specific test case:
normalize(v) * '1 0 0' == v_x * (1.0 / vlen(v))
In DarkPlaces, this is not entirely true as the intermediate value f, storing vlen(v), is taken the reciprocal of while a double, not while a float (the square root is computed as a double in both engines for both builtins).
I suggest changing https://github.com/DarkPlacesEngine/DarkPlaces/blob/master/prvm_cmds.c#L528 from double f to prvm_vec_t f, so the two functions become consistent with each other, and to document this relationship in a comment. Also, possibly the 1.0 used for computing the reciprocal also needs to be cast to (prvm_vec_t).