Fix DIVIDE BY ZERO exception in init_search()

It happens that when d == 0 we calculate:

log(double(0 * 0) / 2)

Unfortunately, log(0) is "illegal" and can generate either a
floating point exception or return a nonsense "huge" value
depending on the platform.

This fixs in the proper way the GCC/ICC rounding difference,
bug was from our side, not in the intel compiler.

Also fixed some few other warnings.

Bug spotted by Richard Lloyd.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>