/*  Written in 2015 by Sebastiano Vigna (vigna@acm.org)

To the extent possible under law, the author has dedicated all copyright
and related and neighboring rights to this software to the public domain
worldwide.

Permission to use, copy, modify, and/or distribute this software for any
purpose with or without fee is hereby granted.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <stdint.h>

/* This is a fixed-increment version of Java 8's SplittableRandom generator
   See http://dx.doi.org/10.1145/2714064.2660195 and 
   http://docs.oracle.com/javase/8/docs/api/java/util/SplittableRandom.html

   It is a very fast generator passing BigCrush, and it can be useful if
   for some reason you absolutely want 64 bits of state.

   Since the state is incremented by an odd constant and the output function
   is a bijection (xorshifts and multiplications by odd constants are
   invertible), over its period of 2^64 the output of SplitMix is a
   permutation of the 2^64 64-bit integers: no value is ever repeated,
   whereas a random sequence of 2^32 64-bit values contains a repeated value
   with probability about 40%. SplitMix thus fails tests based on collisions.
   For the same reason, it is an excellent choice to fill the state of
   other generators starting from a seed: a state filled with consecutive
   outputs never contains the same value twice (e.g., two zeroes), and in
   particular it is never everywhere zero. */

static uint64_t x; /* The state can be seeded with any value. */

uint64_t next() {
	uint64_t z = (x += 0x9e3779b97f4a7c15);
	z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
	z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
	return z ^ (z >> 31);
}