Re: Optimize flag breaks code on many versions of gcc (not all)

[tbp]

On 6/19/06, Richard Guenther <[EMAIL PROTECTED]> wrote:

Using -mfpmath=sse -msse2 is a workaround if you have a processor that supports
SSE2 instructions.  As opposed to -ffloat-store, it works reliably and
with no performance
impact.

Such slab test can be turned into a branchless sequence of SSE
min/max, even for filtering infinities around dir ~= 0; it's much
simpler and efficient to intersect 4 rays against one box at once
though.
Without intrinsics a NaN oblivious version would be like:

static float minf(const float a, const float b) { return (a < b) ? a : b; }
static float maxf(const float a, const float b) { return (a > b) ? a : b; }

bool_t intersect_ray_box(const aabb_t &box, const rt::mono::ray_t
&ray, float &lmin, float &lmax)
{
        float
                l1      = (box.min.x - ray.pos.x) * ray.inv_dir.x,
                l2      = (box.max.x - ray.pos.x) * ray.inv_dir.x;
        lmin    = minf(l1,l2);
        lmax    = maxf(l1,l2);

        l1      = (box.min.y - ray.pos.y) * ray.inv_dir.y;
        l2      = (box.max.y - ray.pos.y) * ray.inv_dir.y;
        lmin    = maxf(minf(l1,l2), lmin);
        lmax    = minf(maxf(l1,l2), lmax);
        
        l1      = (box.min.z - ray.pos.z) * ray.inv_dir.z;
        l2      = (box.max.z - ray.pos.z) * ray.inv_dir.z;
        lmin    = maxf(minf(l1,l2), lmin);
        lmax    = minf(maxf(l1,l2), lmax);

        return (lmax >= lmin) & (lmax >= 0.f);
}