bn_rshift_fixed_top
if (rm != NULL && bn_rshift_fixed_top(rm, snum, norm_shift) == 0)
ret = bn_rshift_fixed_top(r, a, n);
return bn_rshift_fixed_top(out, out, shift);
int bn_rshift_fixed_top(BIGNUM *r, const BIGNUM *a, int n);