Random number generators discussion

First, I would like to inform you an "unofficial" fact of the time benchmarking:
I have compiled mersenne.cpp, Ranrotw.cpp, Mother.cpp and the versions in assembly of them versus ran2 in Linux Redhat 8.1, icc 7.1 compiler, intel xeon 2.8 GHz. The results on time consuming roughly are:

Function time
ran2 = 1
mersenne ~ 0.6
Ranrot ~ 0.7
Mother ~ 1.17
MT Assembly ~ 0.47
Ranrot Asse. ~ floating point exception (why?)
Mother Asse. ~ 0.69

So if the quality is more or less the same in any of them, I would choose the fastest one, which is MT in its assembly version.

Next, I one question concerning the compilation. I compiled MT in C++ version with the above compiler, it posted a warning as follows:

icc ex-ran.cpp
mersenne.cpp(61): warning #68: integer conversion resulted in a change of sign
const uint32 UPPER_MASK = -1L << MERS_R; // upper (32 - MERS_R) bits
^
So it is warning serious? Can I just ignore it or we have to fix it?

Thank you very much for any reply.

Best,
Toan.