On ma, 2016-12-12 at 11:53 +0000, Chris Wilson wrote:
> For testing, we want a reproducible PRNG, a plain linear congruent
> generator is suitable for our very limited selftests.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
<SNIP>
> +++ b/drivers/gpu/drm/lib/drm_rand.c
> @@ -0,0 +1,51 @@
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/types.h>
> +
> +#include "drm_rand.h"
> +
> +u32 drm_lcg_random(u32 *state)
> +{
> + u32 s = *state;
> +
> +#define rol(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
> + s = (s ^ rol(s, 5) ^ rol(s, 24)) + 0x37798849;
> +#undef rol
> +
> + *state = s;
> + return s;
> +}
Do state your source for checking purposes. Code is bound to be copied
and there's no reason to have it good.
> +EXPORT_SYMBOL(drm_lcg_random);
> +
> +int *drm_random_reorder(int *order, int count, u32 *state)
> +{
> + int n;
> +
> + for (n = count-1; n > 1; n--) {
> + int r = drm_lcg_random(state) % (n + 1);
> + if (r != n) {
> + int tmp = order[n];
> + order[n] = order[r];
> + order[r] = tmp;
> + }
> + }
> +
> + return order;
> +}
If you have two items... So definitely add big disclaimers of not being
random, or use some more proven algorithm :)
Regards, Joonas
--
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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