1 files changed, 60 insertions, 0 deletions
diff --git a/tz/difftime.c b/tz/difftime.c
new file mode 100644
index 0000000..ff78f03
--- /dev/null
+++ b/tz/difftime.c
@@ -0,0 +1,60 @@
+/* Return the difference between two timestamps.  */
+
+/*
+** This file is in the public domain, so clarified as of
+** 1996-06-05 by Arthur David Olson.
+*/
+
+/*LINTLIBRARY*/
+
+#include "private.h"	/* for time_t and TYPE_SIGNED */
+
+/* Return -X as a double.  Using this avoids casting to 'double'.  */
+static double
+dminus(double x)
+{
+  return -x;
+}
+
+double
+difftime(time_t time1, time_t time0)
+{
+	/*
+	** If double is large enough, simply convert and subtract
+	** (assuming that the larger type has more precision).
+	*/
+	if (sizeof(time_t) < sizeof(double)) {
+	  double t1 = time1, t0 = time0;
+	  return t1 - t0;
+	}
+
+	/*
+	** The difference of two unsigned values can't overflow
+	** if the minuend is greater than or equal to the subtrahend.
+	*/
+	if (!TYPE_SIGNED(time_t))
+	  return time0 <= time1 ? time1 - time0 : dminus(time0 - time1);
+
+	/* Use uintmax_t if wide enough.  */
+	if (sizeof(time_t) <= sizeof(uintmax_t)) {
+	  uintmax_t t1 = time1, t0 = time0;
+	  return time0 <= time1 ? t1 - t0 : dminus(t0 - t1);
+	}
+
+	/*
+	** Handle cases where both time1 and time0 have the same sign
+	** (meaning that their difference cannot overflow).
+	*/
+	if ((time1 < 0) == (time0 < 0))
+	  return time1 - time0;
+
+	/*
+	** The values have opposite signs and uintmax_t is too narrow.
+	** This suffers from double rounding; attempt to lessen that
+	** by using long double temporaries.
+	*/
+	{
+	  long double t1 = time1, t0 = time0;
+	  return t1 - t0;
+	}
+}