/* logs.h -- define macros for working with logs of unsigned numbers
 *
 * logsum(a, b) is log(exp(a) + exp(b)), computed in such a way as to
 * prevent overflow.  logdif is log(exp(a) - exp(b)).  a must be > b.
 * -1.0 is treated as log(0.0).  logmul(a, b) is log(exp(a) * exp(b)),
 * which is just the sum of a and b unless either is -1.0.
 */
#define	LOGMAXL	(log((double) MAXLONG)) /* log of max long integer	*/

#define	LOG0	(-1.0)			/* clean up the code a little	*/
#define	LOG1	(0.0)
#define	LOG2	(log(2.0))
#define	lsum1(a, b)	((b < LOG1) ? a : (a + log1p(exp(b - a))))
#define	logsum(a, b)	(((a) > (b)) ? lsum1((a), (b)) : lsum1((b), (a)))
#define	logdif(a, b)	(((b) < LOG1) ? (a) : ((a) + log1p(-exp((b) - (a)))))
#define	logmul(a, b)	((((a) < LOG1) || ((b) < LOG1)) ? LOG0 : ((a) + (b)))

#define	logint(a)	(((a) == 0) ? (LOG0) : log((double) (a)))