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/* nbdkit
* Copyright Red Hat
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of Red Hat nor the names of its contributors may be
* used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef NBDKIT_RANDOM_H
#define NBDKIT_RANDOM_H
#include <stdint.h>
/* Generate pseudo-random numbers, quickly, with explicit state.
*
* This is based on the xoshiro/xoroshiro generators by David Blackman
* and Sebastiano Vigna (http://xoshiro.di.unimi.it/). Specifically
* the main PRNG is ‘xoshiro256** 1.0’, and the seed generator is
* ‘splitmix64’.
*
* This does _NOT_ generate cryptographically secure random numbers
* (CSPRNG) and so should not be used when cryptography or security is
* required - use gcrypt if you need those.
*/
/* You can seed ‘struct random_state’ by setting the s[] elements
* directly - but you must NOT set them all to zero. Alternately if
* you have a 64 bit seed, you can call xsrandom to initialize the
* state.
*/
struct random_state {
uint64_t s[4];
};
static inline uint64_t
snext (uint64_t *seed)
{
uint64_t z = (*seed += 0x9e3779b97f4a7c15);
z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
return z ^ (z >> 31);
}
/* Seed the random state from a 64 bit seed. */
static inline void __attribute__ ((__nonnull__ (2)))
xsrandom (uint64_t seed, struct random_state *state)
{
state->s[0] = snext (&seed);
state->s[1] = snext (&seed);
state->s[2] = snext (&seed);
state->s[3] = snext (&seed);
}
static inline uint64_t
rotl (const uint64_t x, int k)
{
/* RWMJ: I checked and GCC 10 emits either ‘rol’ or ‘ror’ correctly
* for this code.
*/
return (x << k) | (x >> (64 - k));
}
/* Returns 64 random bits. Updates the state. */
static inline uint64_t __attribute__ ((__nonnull__ (1)))
xrandom (struct random_state *state)
{
const uint64_t result_starstar = rotl (state->s[1] * 5, 7) * 9;
const uint64_t t = state->s[1] << 17;
state->s[2] ^= state->s[0];
state->s[3] ^= state->s[1];
state->s[1] ^= state->s[2];
state->s[0] ^= state->s[3];
state->s[2] ^= t;
state->s[3] = rotl (state->s[3], 45);
return result_starstar;
}
#endif /* NBDKIT_RANDOM_H */
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