* lib.h (num_fast): Under HAVE_UBSAN, avoid left shifting a negative value, which is diagnosed by ubsan (by default), but is otherwise a documented GCC extension that behaves sanely in the manner one would expect on two's complement machines. * mpi/mpi.c (s_mp_mul_2d): Fix instance of undefined shift equal to the width of the type. This occurs in the case when d == 0. In that case, we try to calculate a 32 or 64 bit full mask by shifting 1 to the left that many times and then subtracting 1. However, the entire code for the fractional shift is not necessary in that case and may be skipped. I'm also removing the unnecesary s_mp_clamp call. If the number is clamped on entry into the function, it stays clamped.