On Fri, Feb 14, 2025 at 09:18:40AM +0100, Markus Theil wrote:

The current Linux PRNG is based on LFSR113, which means:
- needs some warmup rounds to yield better statistical properties
- seeds/initial states must be of certain structure
- does not pass L’Ecuyer's BigCrush in TestU01

While of course, there is no clear "best" PRNG, replace with
Xoshiro256++, which seams to be a sensible replacement, from
todays point of view:
- only needs one bit set to 1 in the seed, needs no warmup, when
  seeded with splitmix64.
- Also has statistical evaluation, like LFSR113.
- Passes BigCrush in TestU01.

The code got smaller, because some edge cases are ruled out now.
I kept the test vectors and adapted them to this RNG.

Signed-off-by: Markus Theil <redacted>

...

...

+/**
+ * prandom_seed_state - set seed for prandom_u32_state().
+ * @state: pointer to state structure to receive the seed.
+ * @seed: arbitrary 64-bit value to use as a seed.
+ *
+ * splitmix64 init as suggested for xoshiro256++
+ * See: https://prng.di.unimi.it/splitmix64.c
+ */
+void prandom_seed_state(struct rnd_state *state, u64 seed)
 {
-	/* Calling RNG ten times to satisfy recurrence condition */
-	prandom_u32_state(state);
-	prandom_u32_state(state);
-	prandom_u32_state(state);
-	prandom_u32_state(state);
-	prandom_u32_state(state);
-	prandom_u32_state(state);
-	prandom_u32_state(state);
-	prandom_u32_state(state);
-	prandom_u32_state(state);
-	prandom_u32_state(state);
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(state->s); ++i) {
+		seed += 0x9e3779b97f4a7c15;
+		u64 z = seed;
+		z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
+		z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
+        state->s[i] = z ^ (z >> 31);

nit: The indentation seems off here.

+	}
 }
+EXPORT_SYMBOL(prandom_seed_state);

...