int BN_sqr(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
	{
	int max,al;
	int ret = 0;
	BIGNUM *tmp,*rr;

#ifdef BN_COUNT
	fprintf(stderr,"BN_sqr %d * %d\n",a->top,a->top);
#endif
	bn_check_top(a);

	al=a->top;
	if (al <= 0)
		{
		r->top=0;
		return 1;
		}

	BN_CTX_start(ctx);
	rr=(a != r) ? r : BN_CTX_get(ctx);
	tmp=BN_CTX_get(ctx);
	if (!rr || !tmp) goto err;

	max = 2 * al; /* Non-zero (from above) */
	if (bn_wexpand(rr,max) == NULL) goto err;

	if (al == 4)
		{
#ifndef BN_SQR_COMBA
		BN_ULONG t[8];
		bn_sqr_normal(rr->d,a->d,4,t);
#else
		bn_sqr_comba4(rr->d,a->d);
#endif
		}
	else if (al == 8)
		{
#ifndef BN_SQR_COMBA
		BN_ULONG t[16];
		bn_sqr_normal(rr->d,a->d,8,t);
#else
		bn_sqr_comba8(rr->d,a->d);
#endif
		}
	else 
		{
#if defined(BN_RECURSION)
		if (al < BN_SQR_RECURSIVE_SIZE_NORMAL)
			{
			BN_ULONG t[BN_SQR_RECURSIVE_SIZE_NORMAL*2];
			bn_sqr_normal(rr->d,a->d,al,t);
			}
		else
			{
			int j,k;

			j=BN_num_bits_word((BN_ULONG)al);
			j=1<<(j-1);
			k=j+j;
			if (al == j)
				{
				if (bn_wexpand(tmp,k*2) == NULL) goto err;
				bn_sqr_recursive(rr->d,a->d,al,tmp->d);
				}
			else
				{
				if (bn_wexpand(tmp,max) == NULL) goto err;
				bn_sqr_normal(rr->d,a->d,al,tmp->d);
				}
			}
#else
		if (bn_wexpand(tmp,max) == NULL) goto err;
		bn_sqr_normal(rr->d,a->d,al,tmp->d);
#endif
		}

	rr->neg=0;
	/* If the most-significant half of the top word of 'a' is zero, then
	 * the square of 'a' will max-1 words. */
	if(a->d[al - 1] == (a->d[al - 1] & BN_MASK2l))
		rr->top = max - 1;
	else
		rr->top = max;
	if (rr != r) BN_copy(r,rr);
	ret = 1;
 err:
	bn_check_top(rr);
	bn_check_top(tmp);
	BN_CTX_end(ctx);
	return(ret);
	}