--- Libc/Libc-1725.40.4/stdtime/FreeBSD/difftime.c
+++ Libc/Libc-391/stdtime/FreeBSD/difftime.c
@@ -1,71 +1,87 @@
 /*
 ** This file is in the public domain, so clarified as of
-** 1996-06-05 by Arthur David Olson.
+** June 5, 1996 by Arthur David Olson (arthur_david_olson@nih.gov).
 */
-
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wunreachable-code"
 
 #include <sys/cdefs.h>
 #ifndef lint
 #ifndef NOID
-static char	elsieid[] __unused = "@(#)difftime.c	8.1";
+static char	elsieid[] __unused = "@(#)difftime.c	7.9";
 #endif /* !defined NOID */
 #endif /* !defined lint */
-__FBSDID("$FreeBSD: src/lib/libc/stdtime/difftime.c,v 1.9 2009/05/23 06:31:50 edwin Exp $");
+__FBSDID("$FreeBSD: src/lib/libc/stdtime/difftime.c,v 1.8 2004/06/14 10:31:52 stefanf Exp $");
 
 /*LINTLIBRARY*/
 
 #include "namespace.h"
-#include "private.h"	/* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */
+#include "private.h"
 #include "un-namespace.h"
 
+/*
+** Algorithm courtesy Paul Eggert (eggert@twinsun.com).
+*/
+
+#ifdef HAVE_LONG_DOUBLE
+#define long_double	long double
+#endif /* defined HAVE_LONG_DOUBLE */
+#ifndef HAVE_LONG_DOUBLE
+#define long_double	double
+#endif /* !defined HAVE_LONG_DOUBLE */
+
 double
-difftime(const time_t time1, const time_t time0)
+difftime(time1, time0)
+const time_t	time1;
+const time_t	time0;
 {
+	time_t	delta;
+	time_t	hibit;
+
+	{
+		time_t		tt;
+		double		d;
+		long_double	ld;
+
+		if (sizeof tt < sizeof d)
+			return (double) time1 - (double) time0;
+		if (sizeof tt < sizeof ld)
+			return (long_double) time1 - (long_double) time0;
+	}
+	if (time1 < time0)
+		return -difftime(time0, time1);
 	/*
-	** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
-	** (assuming that the larger type has more precision).
-	** This is the common real-world case circa 2004.
+	** As much as possible, avoid loss of precision
+	** by computing the difference before converting to double.
 	*/
-	if (sizeof (double) > sizeof (time_t))
-		return (double) time1 - (double) time0;
-	if (!TYPE_INTEGRAL(time_t)) {
-		/*
-		** time_t is floating.
-		*/
-		return time1 - time0;
-	}
-	if (!TYPE_SIGNED(time_t)) {
-		/*
-		** time_t is integral and unsigned.
-		** The difference of two unsigned values can't overflow
-		** if the minuend is greater than or equal to the subtrahend.
-		*/
-		if (time1 >= time0)
-			return time1 - time0;
-		else	return -((double) (time0 - time1));
-	}
+	delta = time1 - time0;
+	if (delta >= 0)
+		return delta;
 	/*
-	** time_t is integral and signed.
-	** Handle cases where both time1 and time0 have the same sign
-	** (meaning that their difference cannot overflow).
+	** Repair delta overflow.
 	*/
-	if ((time1 < 0) == (time0 < 0))
-		return time1 - time0;
+	hibit = (~ (time_t) 0) << (TYPE_BIT(time_t) - 1);
 	/*
-	** time1 and time0 have opposite signs.
-	** Punt if unsigned long is too narrow.
+	** The following expression rounds twice, which means
+	** the result may not be the closest to the true answer.
+	** For example, suppose time_t is 64-bit signed int,
+	** long_double is IEEE 754 double with default rounding,
+	** time1 = 9223372036854775807 and time0 = -1536.
+	** Then the true difference is 9223372036854777343,
+	** which rounds to 9223372036854777856
+	** with a total error of 513.
+	** But delta overflows to -9223372036854774273,
+	** which rounds to -9223372036854774784, and correcting
+	** this by subtracting 2 * (long_double) hibit
+	** (i.e. by adding 2**64 = 18446744073709551616)
+	** yields 9223372036854776832, which
+	** rounds to 9223372036854775808
+	** with a total error of 1535 instead.
+	** This problem occurs only with very large differences.
+	** It's too painful to fix this portably.
+	** We are not alone in this problem;
+	** some C compilers round twice when converting
+	** large unsigned types to small floating types,
+	** so if time_t is unsigned the "return delta" above
+	** has the same double-rounding problem with those compilers.
 	*/
-	if (sizeof (unsigned long) < sizeof (time_t))
-		return (double) time1 - (double) time0;
-	/*
-	** Stay calm...decent optimizers will eliminate the complexity below.
-	*/
-	if (time1 >= 0 /* && time0 < 0 */)
-		return (unsigned long) time1 +
-			(unsigned long) (-(time0 + 1)) + 1;
-	return -(double) ((unsigned long) time0 +
-		(unsigned long) (-(time1 + 1)) + 1);
+	return delta - 2 * (long_double) hibit;
 }
-#pragma clang diagnostic pop