auto import from //depot/cupcake/@135843
diff --git a/libc/tzcode/difftime.c b/libc/tzcode/difftime.c
new file mode 100644
index 0000000..da77977
--- /dev/null
+++ b/libc/tzcode/difftime.c
@@ -0,0 +1,65 @@
+/*
+** This file is in the public domain, so clarified as of
+** 1996-06-05 by Arthur David Olson.
+*/
+
+#ifndef lint
+#ifndef NOID
+static char elsieid[] = "@(#)difftime.c 8.1";
+#endif /* !defined NOID */
+#endif /* !defined lint */
+
+/*LINTLIBRARY*/
+
+#include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */
+
+double
+difftime(time1, time0)
+const time_t time1;
+const time_t time0;
+{
+ /*
+ ** 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.
+ */
+ 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));
+ }
+ /*
+ ** time_t is integral and signed.
+ ** 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;
+ /*
+ ** time1 and time0 have opposite signs.
+ ** Punt if unsigned long is too narrow.
+ */
+ 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);
+}