random - What is the point of the inc variable in the PCG RNG? -

from this code:

// *really* minimal pcg32 code / (c) 2014 m.e. o'neill / pcg-random.org // licensed under apache license 2.0 (no warranty, etc. see website)  typedef struct { uint64_t state;  uint64_t inc; } pcg32_random_t;  uint32_t pcg32_random_r(pcg32_random_t* rng) {     uint64_t oldstate = rng->state;     // advance internal state     rng->state = oldstate * 6364136223846793005ull + (rng->inc|1);     // calculate output function (xsh rr), uses old state max ilp     uint32_t xorshifted = ((oldstate >> 18u) ^ oldstate) >> 27u;     uint32_t rot = oldstate >> 59u;     return (xorshifted >> rot) | (xorshifted << ((-rot) & 31)); } 

what point of rng->inc? never written far can see.

i think it’s seed – stream selector, precise. take @ code on github, pcg32_srandom_r function:

// pcg32_srandom(initstate, initseq) // pcg32_srandom_r(rng, initstate, initseq): //     seed rng.  specified in 2 parts, state initializer , //     sequence selection constant (a.k.a. stream id)  void pcg32_srandom_r(pcg32_random_t* rng, uint64_t initstate, uint64_t initseq) {     rng->state = 0u;     rng->inc = (initseq << 1u) | 1u;     pcg32_random_r(rng);     rng->state += initstate;     pcg32_random_r(rng); } 

there’s more streams on the pcg website.