Simpler alternative to timegm(), thanks to Garrett Wollman.

SVN-Revision: 52

diff --git a/libarchive/archive_read_support_format_iso9660.c b/libarchive/archive_read_support_format_iso9660.c
index ee9831b90be9ef9c91e6fe9186f3c0cc6eb67572..08d64ed78bf44f819cc22892e61f92c1a20953e4 100644 (file)
--- a/libarchive/archive_read_support_format_iso9660.c
+++ b/libarchive/archive_read_support_format_iso9660.c
@@ -1046,51 +1046,22 @@ isodate17(const unsigned char *v)
        return (time_from_tm(&tm));
 }
 
-/*
- * timegm() converts a struct tm to a time_t, except it isn't standard,
- * so I provide my own function here that (ideally) is just a wrapper
- * for timegm().
- */
 static time_t
 time_from_tm(struct tm *t)
 {
 #if HAVE_TIMEGM
+       /* Use platform timegm() if available. */
        return (timegm(t));
-#elif HAVE_STRUCT_TM_TM_GMTOFF
-       /*
-        * Unfortunately, timegm() isn't standard.  The standard
-        * mktime() function is a close match, except that it uses
-        * local timezone instead of GMT.  You can compensate for
-        * this by adding the timezone and DST offsets back in, at
-        * the cost of two calls to mktime().
-        */
-       mktime(t); /* Normalize the time and get the TZ offset. */
-       t->tm_sec += t->tm_gmtoff; /* Try to adjust for the timezone and DST.*/
-       if (t->tm_isdst)
-               t->tm_hour -= 1;
-       return (mktime(t)); /* Re-convert. */
-#elif defined(HAVE_SETENV) && defined(HAVE_UNSETENV) && defined(HAVE_TZSET)
-       /* No timegm() and no tm_gmtoff, let's try forcing mktime() to UTC. */
-       time_t ret;
-       char *tz;
-
-       /* Reset the timezone, remember the old one. */
-       tz = getenv("TZ");
-       setenv("TZ", "UTC 0", 1);
-       tzset();
-
-       ret = mktime(t);
-
-       /* Restore the previous timezone. */
-       if (tz)
-           setenv("TZ", tz, 1);
-       else
-           unsetenv("TZ");
-       tzset();
-       return ret;
 #else
-       /* <sigh> We have no choice but to use localtime instead of UTC. */
-       return (mktime(t));
+       /* Else use direct calculation using POSIX assumptions. */
+       /* First, fix up tm_yday based on the year/month/day. */
+       mktime(t);
+       /* Then we can compute timegm() from first principles. */
+       return (t->tm_sec + t->tm_min * 60 + t->tm_hour * 3600
+           + t->tm_yday * 86400 + (t->tm_year - 70) * 31536000
+           + ((t->tm_year - 69) / 4) * 86400 -
+           ((t->tm_year - 1) / 100) * 86400
+           + ((t->tm_year + 299) / 400) * 86400);
 #endif
 }