float[] → Vertex[] – decreases performance by 1000%

[H. S. Teoh]

On Tue, Jul 24, 2012 at 08:57:08PM +0200, bearophile wrote:
> David:
> 
> >align(1) struct Vertex {
> >    float x;
> >    float y;
> >    float z;
> >    float nx;
> >    float ny;
> >    float nz;
> >    float u_terrain;
> >    float v_terrain;
> >    float u_biome;
> >    float v_biome;
> >}
> >
> >Everything is still a float, so it's easier. Nothing wrong with
> >that or? Well this change decreases my performance by 1000%.
> 
> Aligning floats to 1 byte doesn't seem a good idea. Try to remove
> the aling(1).
[...]

I agree. I don't know how the CPU handles misaligned floats, but from
what I understand, it will do two loads to fetch the two word-aligned
parts of the float, and then assemble it together. This may be what's
causing the slowdown.


T

-- 
Маленькие детки - маленькие бедки.