tmp= &(ctx.bn[ctx.tos++]);
BN_CTX_start(&ctx); tmp = BN_CTX_get(&ctx);
static int compute_key(unsigned char *key, BIGNUM *pub_key, DH *dh)	{	BN_CTX ctx;	BN_MONT_CTX *mont;	BIGNUM *tmp;	int ret= -1;	BN_CTX_init(&ctx);	tmp= &(ctx.bn[ctx.tos++]);		if (dh->priv_key == NULL)		{		DHerr(DH_F_DH_COMPUTE_KEY,DH_R_NO_PRIVATE_VALUE);		goto err;		}	if ((dh->method_mont_p == NULL) && (dh->flags & DH_FLAG_CACHE_MONT_P))		{		if ((dh->method_mont_p=(char *)BN_MONT_CTX_new()) != NULL)			if (!BN_MONT_CTX_set((BN_MONT_CTX *)dh->method_mont_p,				dh->p,&ctx)) goto err;		}	mont=(BN_MONT_CTX *)dh->method_mont_p;	if (!dh->meth->bn_mod_exp(dh, tmp,pub_key,dh->priv_key,dh->p,&ctx,mont))		{		DHerr(DH_F_DH_COMPUTE_KEY,ERR_R_BN_LIB);		goto err;		}	ret=BN_bn2bin(tmp,key);err:	BN_CTX_free(&ctx);	return(ret);	}