null character without reason in written files

[FX]

> I know it but that's not a RNG with good statistical properties.

The Fortran standard makes no guarantees on the statistical properties of the PRNG. Obviously, there is no single “perfect” PRNG, so use something that checks the boxes you need checked!

But, I wanted to stress that gfortran’s implementation of RANDOM_NUMBER, as documented at http://gcc.gnu.org/onlinedocs/gfortran/RANDOM_005fNUMBER.html , relies on pretty robust and certainly well-studied PRNG: George Marsaglia's KISS. It has been so since a long time now, probably somewhere around version 4.3.

In particular, it does not show the “obvious” telltale signs of bias.

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FX