The current implementation of PCGSource has a number of missing features, mostly related to control over the seeding process. The Seed() method even has a TODO in it:

// Seed uses the provided seed value to initialize the generator to a deterministic state.
func (pcg *PCGSource) Seed(seed uint64) {
	pcg.low = seed
	pcg.high = seed // TODO: What is right?
}

Similarly, there's no way to get access to the current seed data.

Bikeshed Color 1

I propose adding a new function and two methods:

func NewPCGSource(high, low uint64) *PCGSource
func (pcg *PCGSource) SeedPCG(high, low uint64)
func (pcg *PCGSource) PCG() (high, low uint64)

This would give much greater control over the source.

Bikeshed Color 2

Alternatively, I recently copied the existing implementation in order to remove the internal state from it completely for a somewhat specific use case. I replaced the entire system with single function, func Next(high, low uint64) (n, nhigh, nlow uint64), that gave me full control over the generation.

If such a function was added, the existing implementation could easily be changed to just call any such function instead:

func (pcg *PCGSource) Uint64() (n uint64) {
  n, pcg.high, pcg.low = NextPCG(pcg.high, pcg.low)
  return
}

Summary

I'm bikeshedding a bit, but my only point is that I'd like some greater control over the PCGSource implementation's seeding process.