Signed 16.16 fixed point multiply.

mulx.c

static inline fixed mulx_fast(fixed x, fixed y){return (fixed){(x.asint >> 8) * (y.asint >> 8)};}

static inline fixed mulx(fixed x, fixed y){
	bool neg = (x.asint ^ y.asint) < 0;
	union {
		u32 asint;
		struct {u16 hi, lo;};
	} _x, _y;
	
	if(x.asint >= 0) _x.asint = x.asint; else _x.asint = -x.asint;
	if(y.asint >= 0) _y.asint = y.asint; else _y.asint = -y.asint;
	
	u32 z = 0;
	z += (_x.hi*_y.hi) << 16;
	z += (_x.hi*_y.lo);
	z += (_x.lo*_y.hi);
	z += (_x.lo*_y.lo) >> 16;
	return (fixed){neg ? -z : z};
}