From 43af5893fb69d3de9e98dffba58f14308eddb83a Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Mon, 19 Oct 2020 21:34:40 +1100
Subject: [PATCH] AP_RTC: added mktime(), used by AP_Filesystem and AP_GPS

---
 libraries/AP_RTC/AP_RTC.cpp | 43 +++++++++++++++++++++++++++++++++++++
 libraries/AP_RTC/AP_RTC.h   |  3 +++
 2 files changed, 46 insertions(+)

diff --git a/libraries/AP_RTC/AP_RTC.cpp b/libraries/AP_RTC/AP_RTC.cpp
index e765a4e986..ef4af285fb 100644
--- a/libraries/AP_RTC/AP_RTC.cpp
+++ b/libraries/AP_RTC/AP_RTC.cpp
@@ -3,6 +3,7 @@
 #include <AP_HAL/AP_HAL.h>
 #include <AP_Math/AP_Math.h>
 #include <GCS_MAVLink/GCS.h>
+#include <time.h>
 
 extern const AP_HAL::HAL& hal;
 
@@ -205,6 +206,48 @@ uint32_t AP_RTC::get_time_utc(int32_t hour, int32_t min, int32_t sec, int32_t ms
 }
 
 
+/*
+  mktime replacement from Samba
+ */
+time_t AP_RTC::mktime(const struct tm *t)
+{
+    time_t epoch = 0;
+    int n;
+    int mon [] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }, y, m, i;
+    const unsigned MINUTE = 60;
+    const unsigned HOUR = 60*MINUTE;
+    const unsigned DAY = 24*HOUR;
+    const unsigned YEAR = 365*DAY;
+
+    if (t->tm_year < 70) {
+        return (time_t)-1;
+    }
+
+    n = t->tm_year + 1900 - 1;
+    epoch = (t->tm_year - 70) * YEAR +
+            ((n / 4 - n / 100 + n / 400) - (1969 / 4 - 1969 / 100 + 1969 / 400)) * DAY;
+
+    y = t->tm_year + 1900;
+    m = 0;
+
+    for (i = 0; i < t->tm_mon; i++) {
+        epoch += mon [m] * DAY;
+        if (m == 1 && y % 4 == 0 && (y % 100 != 0 || y % 400 == 0)) {
+            epoch += DAY;
+        }
+
+        if (++m > 11) {
+            m = 0;
+            y++;
+        }
+    }
+
+    epoch += (t->tm_mday - 1) * DAY;
+    epoch += t->tm_hour * HOUR + t->tm_min * MINUTE + t->tm_sec;
+
+    return epoch;
+}
+
 // singleton instance
 AP_RTC *AP_RTC::_singleton;
 
diff --git a/libraries/AP_RTC/AP_RTC.h b/libraries/AP_RTC/AP_RTC.h
index ea904d82bb..36ac3def04 100644
--- a/libraries/AP_RTC/AP_RTC.h
+++ b/libraries/AP_RTC/AP_RTC.h
@@ -44,6 +44,9 @@ public:
 
     uint32_t get_time_utc(int32_t hour, int32_t min, int32_t sec, int32_t ms);
 
+    // replacement for mktime()
+    static time_t mktime(const struct tm *t);
+
     // get singleton instance
     static AP_RTC *get_singleton() {
         return _singleton;