Mersenne Twister (MT19937) -- the notice MPAS-Model v8.4.2 carries

src/hexcore/mpasphys/rrtmg_sw_v842.py ports the MersenneTwister module in
src/core_atmosphere/physics/physics_wrf/module_ra_rrtmg_lw.F of MPAS-Model
v8.4.2 (commit f34984b2c89353cf31c235b08d3b4acd96b37bb3), which RRTMG uses
for its cloud sampling. That module is a Fortran 95 implementation by Robert
Pincus (NOAA-CIRES Climate Diagnostics Center) of the MT19937 C program by
Takuji Nishimura and Makoto Matsumoto. Its documentation reproduces the
original program's notice, which is reproduced here verbatim without the
Fortran comment markers:

   A C-program for MT19937, with initialization improved 2002/2/10.
   Coded by Takuji Nishimura and Makoto Matsumoto.
   This is a faster version by taking Shawn Cokus's optimization,
   Matthe Bellew's simplification, Isaku Wada's real version.

   Before using, initialize the state by using init_genrand(seed)
   or init_by_array(init_key, key_length).

   Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
   All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:

     1. Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.

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     3. The names of its contributors may not be used to endorse or promote
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