if (BN_lsw(A) & BN_lsw(B) & 2)
if ((A->neg ? ~BN_lsw(A) : BN_lsw(A)) & BN_lsw(B) & 2)
int BN_kronecker(const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx)	{	int i;	int ret;	int err = 0;	BIGNUM *A, *B, *tmp;	/* In 'tab', only odd-indexed entries are relevant:	 * For any odd BIGNUM n,	 *     tab[BN_lsw(n) & 7]	 * is $(-1)^{(n^2-1)/8}$ (using TeX notation).	 * Note that the sign of n does not matter.	 */	static const int tab[8] = {0, 1, 0, -1, 0, -1, 0, 1};	BN_CTX_start(ctx);	A = BN_CTX_get(ctx);	B = BN_CTX_get(ctx);	if (B == NULL) goto end;		err = !BN_copy(A, a);	if (err) goto end;	err = !BN_copy(B, b);	if (err) goto end;	/*	 * Kronecker symbol, imlemented according to Henri Cohen,	 * "A Course in Computational Algebraic Number Theory"	 * (algorithm 1.4.10).	 */	/* Cohen's step 1: */	if (BN_is_zero(B))		{		ret = BN_abs_is_word(A, 1);		goto end; 		}		/* Cohen's step 2: */	if (!BN_is_odd(A) && !BN_is_odd(B))		{		ret = 0;		goto end;		}	/* now  B  is non-zero */	i = 0;	while (!BN_is_bit_set(B, i))		i++;	err = !BN_rshift(B, B, i);	if (err) goto end;	if (i & 1)		{		/* i is odd */		/* (thus  B  was even, thus  A  must be odd!)  */		/* set 'ret' to $(-1)^{(A^2-1)/8}$ */		ret = tab[BN_lsw(A) & 7];		}	else		{		/* i is even */		ret = 1;		}		if (B->neg)		{		B->neg = 0;		if (A->neg)			ret = -ret;		}	/* now  B  is positive and odd, so what remains to be done is	 * to compute the Jacobi symbol  (A/B)  and multiply it by 'ret' */	while (1)		{		/* Cohen's step 3: */		/*  B  is positive and odd */		if (BN_is_zero(A))			{			ret = BN_is_one(B) ? ret : 0;			goto end;			}		/* now  A  is non-zero */		i = 0;		while (!BN_is_bit_set(A, i))			i++;		err = !BN_rshift(A, A, i);		if (err) goto end;		if (i & 1)			{			/* i is odd */			/* multiply 'ret' by  $(-1)^{(B^2-1)/8}$ */			ret = ret * tab[BN_lsw(B) & 7];			}			/* Cohen's step 4: */		/* multiply 'ret' by  $(-1)^{(A-1)(B-1)/4}$ */		if (BN_lsw(A) & BN_lsw(B) & 2)			ret = -ret;				/* (A, B) := (B mod |A|, |A|) */		err = !BN_nnmod(B, B, A, ctx);		if (err) goto end;		tmp = A; A = B; B = tmp;		tmp->neg = 0;		}	 end:	BN_CTX_end(ctx);	if (err)		return -2;	else		return ret;	}