bn_check_top(a);
int BN_set_bit(BIGNUM *a, int n)	{	int i,j,k;	i=n/BN_BITS2;	j=n%BN_BITS2;	if (a->top <= i)		{		if (bn_wexpand(a,i+1) == NULL) return(0);		for(k=a->top; k<i+1; k++)			a->d[k]=0;		a->top=i+1;		}	a->d[i]|=(((BN_ULONG)1)<<j);	return(1);	}