I'm worried that when people do things of their own choice, somebody could get hurt.  I hear this is a common worry.

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libgcrypt/mpi/mpi-internal.h:113
#define MPN_NORMALIZE(d, n)  \                                                       do {                       \                                                         while( (n) > 0 ) {     \                                                             if( (d)[(n)-1] ) \                                                                   break;         \                                                             (n)--;             \
        }                      \
    } while(0)

It looks like MPN_NORMALIZE is boilerplate that rewinds its second parameter to skip extra falsey elements at the end of its first.