int BN_generate_prime_ex(BIGNUM *ret, int bits, int safe,
	const BIGNUM *add, const BIGNUM *rem, BN_GENCB *cb)
	{
	BIGNUM *t;
	int found=0;
	int i,j,c1=0;
	BN_CTX *ctx;
	int checks = BN_prime_checks_for_size(bits);

	ctx=BN_CTX_new();
	if (ctx == NULL) goto err;
	BN_CTX_start(ctx);
	t = BN_CTX_get(ctx);
	if(!t) goto err;
loop: 
	/* make a random number and set the top and bottom bits */
	if (add == NULL)
		{
		if (!probable_prime(ret,bits)) goto err;
		}
	else
		{
		if (safe)
			{
			if (!probable_prime_dh_safe(ret,bits,add,rem,ctx))
				 goto err;
			}
		else
			{
			if (!probable_prime_dh(ret,bits,add,rem,ctx))
				goto err;
			}
		}
	/* if (BN_mod_word(ret,(BN_ULONG)3) == 1) goto loop; */
	if(!BN_GENCB_call(cb, 0, c1++))
		/* aborted */
		goto err;

	if (!safe)
		{
		i=BN_is_prime_fasttest_ex(ret,checks,ctx,0,cb);
		if (i == -1) goto err;
		if (i == 0) goto loop;
		}
	else
		{
		/* for "safe prime" generation,
		 * check that (p-1)/2 is prime.
		 * Since a prime is odd, We just
		 * need to divide by 2 */
		if (!BN_rshift1(t,ret)) goto err;

		for (i=0; i<checks; i++)
			{
			j=BN_is_prime_fasttest_ex(ret,1,ctx,0,cb);
			if (j == -1) goto err;
			if (j == 0) goto loop;

			j=BN_is_prime_fasttest_ex(t,1,ctx,0,cb);
			if (j == -1) goto err;
			if (j == 0) goto loop;

			if(!BN_GENCB_call(cb, 2, c1-1))
				goto err;
			/* We have a safe prime test pass */
			}
		}
	/* we have a prime :-) */
	found = 1;
err:
	if (ctx != NULL)
		{
		BN_CTX_end(ctx);
		BN_CTX_free(ctx);
		}
	bn_check_top(ret);
	return found;
	}