From a9ce4dc76cbc338ea1812bd37663593e658f8f1e Mon Sep 17 00:00:00 2001
From: Oliver Schmidt <ol.sc@web.de>
Date: Thu, 2 Aug 2018 17:12:12 +0200
Subject: [PATCH] "Inverted" time_t value handling.

So far time_t values were interpreted as local time values. However, usually time_t values are to be interpreted as "seconds since 1 Jan 1970 in UTC". Therefore all logic handling time_t values has to be changed.

- So far gmtime() called localtime() with an adjusted time_t, now localtime() calls gmtime() with an adjusted time_t.
- mktime() has to do "the opposite" of localtime(), to keep it that way mktime() does now the inverse adjustment made by localtime().
- All currently present time() implementations internally call mktime() so they don't require individual adjustments.
---
 libsrc/common/gmtime.c    | 28 +++++++++++++++++++---------
 libsrc/common/localtime.c | 27 ++++++---------------------
 libsrc/common/mktime.c    |  3 ++-
 3 files changed, 27 insertions(+), 31 deletions(-)

diff --git a/libsrc/common/gmtime.c b/libsrc/common/gmtime.c
index 1a2536c5f..85e9de3d0 100644
--- a/libsrc/common/gmtime.c
+++ b/libsrc/common/gmtime.c
@@ -45,19 +45,29 @@
 
 struct tm* __fastcall__ gmtime (const time_t* timep)
 {
+    static struct tm timebuf;
     time_t t;
 
-    /* Check for a valid time spec */
-    if (timep == 0) {
+    /* Check the argument */
+    if (timep == 0 || (long) (t = *timep) < 0) {
+        /* Invalid arg */
         return 0;
     }
 
-    /* Get the time and correct for the time zone offset */
-    t = *timep + _tz.timezone;
-
-    /* Use localtime for conversion */
-    return localtime (&t);
-}
-
+    /* Since our ints are just 16 bits, split the given time into seconds,
+    ** hours and days. Each of the values will fit in a 16 bit variable.
+    ** The mktime routine will then do the rest.
+    */
+    timebuf.tm_sec  = t % 3600;
+    timebuf.tm_min  = 0;
+    timebuf.tm_hour = (t / 3600) % 24;
+    timebuf.tm_mday = (t / (3600UL * 24UL)) + 1;
+    timebuf.tm_mon  = 0;
+    timebuf.tm_year = 70;       /* Base value is 1/1/1970 */
 
+    /* Call mktime to do the final conversion */
+    mktime (&timebuf);
 
+    /* Return the result */
+    return &timebuf;
+}
diff --git a/libsrc/common/localtime.c b/libsrc/common/localtime.c
index cc6298f8c..48931ea62 100644
--- a/libsrc/common/localtime.c
+++ b/libsrc/common/localtime.c
@@ -45,31 +45,16 @@
 
 struct tm* __fastcall__ localtime (const time_t* timep)
 {
-    static struct tm timebuf;
     time_t t;
 
-    /* Check the argument */
-    if (timep == 0 || (long) (t = *timep) < 0) {
-        /* Invalid arg */
+    /* Check for a valid time spec */
+    if (timep == 0) {
         return 0;
     }
 
-    /* Since our ints are just 16 bits, split the given time into seconds,
-    ** hours and days. Each of the values will fit in a 16 bit variable.
-    ** The mktime routine will then do the rest.
-    */
-    timebuf.tm_sec  = t % 3600;
-    timebuf.tm_min  = 0;
-    timebuf.tm_hour = (t / 3600) % 24;
-    timebuf.tm_mday = (t / (3600UL * 24UL)) + 1;
-    timebuf.tm_mon  = 0;
-    timebuf.tm_year = 70;       /* Base value is 1/1/1970 */
+    /* Get the time and correct for the time zone offset */
+    t = *timep + _tz.timezone;
 
-    /* Call mktime to do the final conversion */
-    mktime (&timebuf);
-
-    /* Return the result */
-    return &timebuf;
+    /* Use gmtime for conversion */
+    return gmtime (&t);
 }
-
-
diff --git a/libsrc/common/mktime.c b/libsrc/common/mktime.c
index 423727751..275589dbb 100644
--- a/libsrc/common/mktime.c
+++ b/libsrc/common/mktime.c
@@ -180,7 +180,8 @@ time_t __fastcall__ mktime (register struct tm* TM)
     return DayCount * 86400UL +
            ((unsigned) TM->tm_hour) * 3600UL +
            ((unsigned) TM->tm_min) * 60U +
-           ((unsigned) TM->tm_sec);
+           ((unsigned) TM->tm_sec) -
+           _tz.timezone;
 
 Error:
     /* Error exit */
-- 
2.39.5