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      1 /*	$NetBSD: drm_random.c,v 1.2 2021/12/18 23:45:31 riastradh Exp $	*/
      2 
      3 // SPDX-License-Identifier: GPL-2.0
      4 #include <sys/cdefs.h>
      5 __KERNEL_RCSID(0, "$NetBSD: drm_random.c,v 1.2 2021/12/18 23:45:31 riastradh Exp $");
      6 
      7 #include <linux/bitops.h>
      8 #include <linux/kernel.h>
      9 #include <linux/random.h>
     10 #include <linux/slab.h>
     11 #include <linux/types.h>
     12 
     13 #include "drm_random.h"
     14 
     15 static inline u32 drm_prandom_u32_max_state(u32 ep_ro, struct rnd_state *state)
     16 {
     17 	return upper_32_bits((u64)prandom_u32_state(state) * ep_ro);
     18 }
     19 
     20 void drm_random_reorder(unsigned int *order, unsigned int count,
     21 			struct rnd_state *state)
     22 {
     23 	unsigned int i, j;
     24 
     25 	for (i = 0; i < count; ++i) {
     26 		BUILD_BUG_ON(sizeof(unsigned int) > sizeof(u32));
     27 		j = drm_prandom_u32_max_state(count, state);
     28 		swap(order[i], order[j]);
     29 	}
     30 }
     31 EXPORT_SYMBOL(drm_random_reorder);
     32 
     33 unsigned int *drm_random_order(unsigned int count, struct rnd_state *state)
     34 {
     35 	unsigned int *order, i;
     36 
     37 	order = kmalloc_array(count, sizeof(*order), GFP_KERNEL);
     38 	if (!order)
     39 		return order;
     40 
     41 	for (i = 0; i < count; i++)
     42 		order[i] = i;
     43 
     44 	drm_random_reorder(order, count, state);
     45 	return order;
     46 }
     47 EXPORT_SYMBOL(drm_random_order);
     48