Re: [gfortran] PATCH -- Fix segfault in RANDOM_SEED.

[Tobias Schlüter <tobias dot schlueter at physik dot uni-muenchen dot de>]

Steve Kargl wrote:
> > >    CALL  RANDOM_SEED (PUT=SEED1)
> > >    CALL  RANDOM_SEED (GET=SEED2)
> > >    CALL  RANDOM_NUMBER (X1)
> > >    CALL  RANDOM_SEED (PUT=SEED2)
> > >    CALL  RANDOM_NUMBER (X2)
> > >
> > >  X2 equals X1.
> >
> > Just XOR the seed before filling in seed2 (in RANDOM_SEED) should do the 
> > trick, I believe.

I don't know what you meant precisely in your e-mail, I'll just walk 
through my suggestion in a pseudo-debugging manner:

    CALL  RANDOM_SEED (PUT=SEED1)

	-> seed = SEED1 ^ MASK ('seed' denotes the RNG's internal seed)

    CALL  RANDOM_SEED (GET=SEED2)

	-> SEED2 = seed ^ MASK = SEED1 ^ MASK ^ MASK = SEED1   (*)

    CALL  RANDOM_NUMBER (X1)
	
	-> X1 = something

    CALL  RANDOM_SEED (PUT=SEED2)

	-> seed = SEED2 ^ MASK = SEED1 ^ MASK (by (*))

    CALL  RANDOM_NUMBER (X2)

	-> X2 = X1

Which is what we want. The trick is of course that the operation (.)^X^X 
  is the identity operation.

Perhaps I have missed something. As I said, I have other stuff to attend 
right now, so I can't double-check this. I'm sorry for wasting your 
time, if I'm wrong.

- Tobi