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 <theil.markus@xxxxxxxxx> ... > diff --git a/lib/random32.c b/lib/random32.c ... > +/** > + * 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); ...
