In C, signed integer overflow is undefined behavior. Thus, the
compiler is allowed to assume that it will not occur. In the check for
an overflow, the developer assumes that the signed integer of type
time_t will wrap around if it overflows. However, this behavior is
undefined in the C standard. Thus, when the compiler sees this,
it simplifies t + delta < t to delta < 0. Since delta > 0 and
delta < 0 can't both be true, the entire if statement is optimized
out under certain optimization levels. Thus, the parsedate function
would return PARSEDATE_OK with an undefined value in the time,
instead of return -1 = PARSEDATE_FAIL.

---
 lib/parsedate.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/parsedate.c b/lib/parsedate.c
index 1ddd008..b32be8f 100644
--- a/lib/parsedate.c
+++ b/lib/parsedate.c
@@ -526,7 +526,7 @@ static int parsedate(const char *date, time_t *output)
     /* Add the time zone diff between local time zone and GMT. */
     long delta = (long)(tzoff!=-1?tzoff:0);
 
-    if((delta>0) && (t + delta < t))
+    if((delta>0) && t > LONG_MAX  - delta)
       return -1; /* time_t overflow */
 
     t += delta;
-- 
1.7.9.5
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