int BN_mod_exp2_mont(BIGNUM *rr, const BIGNUM *a1, const BIGNUM *p1,
	const BIGNUM *a2, const BIGNUM *p2, const BIGNUM *m,
	BN_CTX *ctx, BN_MONT_CTX *in_mont)
	{
	int i,j,bits,b,bits1,bits2,ret=0,wpos1,wpos2,window1,window2,wvalue1,wvalue2;
	int r_is_one=1;
	BIGNUM *d,*r;
	const BIGNUM *a_mod_m;
	/* Tables of variables obtained from 'ctx' */
	BIGNUM *val1[TABLE_SIZE], *val2[TABLE_SIZE];
	BN_MONT_CTX *mont=NULL;

	bn_check_top(a1);
	bn_check_top(p1);
	bn_check_top(a2);
	bn_check_top(p2);
	bn_check_top(m);

	if (!(m->d[0] & 1))
		{
		BNerr(BN_F_BN_MOD_EXP2_MONT,BN_R_CALLED_WITH_EVEN_MODULUS);
		return(0);
		}
	bits1=BN_num_bits(p1);
	bits2=BN_num_bits(p2);
	if ((bits1 == 0) && (bits2 == 0))
		{
		ret = BN_one(rr);
		return ret;
		}
	
	bits=(bits1 > bits2)?bits1:bits2;

	BN_CTX_start(ctx);
	d = BN_CTX_get(ctx);
	r = BN_CTX_get(ctx);
	val1[0] = BN_CTX_get(ctx);
	val2[0] = BN_CTX_get(ctx);
	if(!d || !r || !val1[0] || !val2[0]) goto err;

	if (in_mont != NULL)
		mont=in_mont;
	else
		{
		if ((mont=BN_MONT_CTX_new()) == NULL) goto err;
		if (!BN_MONT_CTX_set(mont,m,ctx)) goto err;
		}

	window1 = BN_window_bits_for_exponent_size(bits1);
	window2 = BN_window_bits_for_exponent_size(bits2);

	/*
	 * Build table for a1:   val1[i] := a1^(2*i + 1) mod m  for i = 0 .. 2^(window1-1)
	 */
	if (a1->neg || BN_ucmp(a1,m) >= 0)
		{
		if (!BN_mod(val1[0],a1,m,ctx))
			goto err;
		a_mod_m = val1[0];
		}
	else
		a_mod_m = a1;
	if (BN_is_zero(a_mod_m))
		{
		BN_zero(rr);
		ret = 1;
		goto err;
		}

	if (!BN_to_montgomery(val1[0],a_mod_m,mont,ctx)) goto err;
	if (window1 > 1)
		{
		if (!BN_mod_mul_montgomery(d,val1[0],val1[0],mont,ctx)) goto err;

		j=1<<(window1-1);
		for (i=1; i<j; i++)
			{
			if(((val1[i] = BN_CTX_get(ctx)) == NULL) ||
					!BN_mod_mul_montgomery(val1[i],val1[i-1],
						d,mont,ctx))
				goto err;
			}
		}


	/*
	 * Build table for a2:   val2[i] := a2^(2*i + 1) mod m  for i = 0 .. 2^(window2-1)
	 */
	if (a2->neg || BN_ucmp(a2,m) >= 0)
		{
		if (!BN_mod(val2[0],a2,m,ctx))
			goto err;
		a_mod_m = val2[0];
		}
	else
		a_mod_m = a2;
	if (BN_is_zero(a_mod_m))
		{
		BN_zero(rr);
		ret = 1;
		goto err;
		}
	if (!BN_to_montgomery(val2[0],a_mod_m,mont,ctx)) goto err;
	if (window2 > 1)
		{
		if (!BN_mod_mul_montgomery(d,val2[0],val2[0],mont,ctx)) goto err;

		j=1<<(window2-1);
		for (i=1; i<j; i++)
			{
			if(((val2[i] = BN_CTX_get(ctx)) == NULL) ||
					!BN_mod_mul_montgomery(val2[i],val2[i-1],
						d,mont,ctx))
				goto err;
			}
		}


	/* Now compute the power product, using independent windows. */
	r_is_one=1;
	wvalue1=0;  /* The 'value' of the first window */
	wvalue2=0;  /* The 'value' of the second window */
	wpos1=0;    /* If wvalue1 > 0, the bottom bit of the first window */
	wpos2=0;    /* If wvalue2 > 0, the bottom bit of the second window */

	if (!BN_to_montgomery(r,BN_value_one(),mont,ctx)) goto err;
	for (b=bits-1; b>=0; b--)
		{
		if (!r_is_one)
			{
			if (!BN_mod_mul_montgomery(r,r,r,mont,ctx))
				goto err;
			}
		
		if (!wvalue1)
			if (BN_is_bit_set(p1, b))
				{
				/* consider bits b-window1+1 .. b for this window */
				i = b-window1+1;
				while (!BN_is_bit_set(p1, i)) /* works for i<0 */
					i++;
				wpos1 = i;
				wvalue1 = 1;
				for (i = b-1; i >= wpos1; i--)
					{
					wvalue1 <<= 1;
					if (BN_is_bit_set(p1, i))
						wvalue1++;
					}
				}
		
		if (!wvalue2)
			if (BN_is_bit_set(p2, b))
				{
				/* consider bits b-window2+1 .. b for this window */
				i = b-window2+1;
				while (!BN_is_bit_set(p2, i))
					i++;
				wpos2 = i;
				wvalue2 = 1;
				for (i = b-1; i >= wpos2; i--)
					{
					wvalue2 <<= 1;
					if (BN_is_bit_set(p2, i))
						wvalue2++;
					}
				}

		if (wvalue1 && b == wpos1)
			{
			/* wvalue1 is odd and < 2^window1 */
			if (!BN_mod_mul_montgomery(r,r,val1[wvalue1>>1],mont,ctx))
				goto err;
			wvalue1 = 0;
			r_is_one = 0;
			}
		
		if (wvalue2 && b == wpos2)
			{
			/* wvalue2 is odd and < 2^window2 */
			if (!BN_mod_mul_montgomery(r,r,val2[wvalue2>>1],mont,ctx))
				goto err;
			wvalue2 = 0;
			r_is_one = 0;
			}
		}
	BN_from_montgomery(rr,r,mont,ctx);
	ret=1;
err:
	if ((in_mont == NULL) && (mont != NULL)) BN_MONT_CTX_free(mont);
	BN_CTX_end(ctx);
	bn_check_top(rr);
	return(ret);
	}