Introduce gmtime.c and use it in the AS3514 RTC driver

Change-Id: I00a09ae28a68f8153fb8fa854fea741ddfb0bf09
Reviewed-on: http://gerrit.rockbox.org/175
Tested-by: Bertrik Sikken <bertrik@sikken.nl>
Reviewed-by: Michael Sevakis <jethead71@rockbox.org>
Reviewed-by: Rafaël Carré <rafael.carre@gmail.com>

firmware/libc/gmtime.c

@@ -0,0 +1,112 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2012 by Bertrik Sikken
+ *
+ * Based on code from: rtc_as3514.c
+ * Copyright (C) 2007 by Barry Wardell
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#include <stdbool.h>
+#include "time.h"
+
+#define MINUTE_SECONDS      60
+#define HOUR_SECONDS        3600
+#define DAY_SECONDS         86400
+#define WEEK_SECONDS        604800
+#define YEAR_SECONDS        31536000
+#define LEAP_YEAR_SECONDS   31622400
+
+/* Days in each month */
+static int days_in_month[] =
+    {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
+
+static inline bool is_leapyear(int year)
+{
+    return (((year%4)==0) && (((year%100)!=0) || ((year%400)==0)));
+}
+
+struct tm *gmtime(const time_t *timep)
+{
+    static struct tm time;
+    return gmtime_r(timep, &time);
+}
+
+struct tm *gmtime_r(const time_t *timep, struct tm *tm)
+{
+    time_t seconds = *timep;
+    int year, i, mday, hour, min;
+
+    /* weekday */
+    tm->tm_wday = ((seconds % WEEK_SECONDS) / DAY_SECONDS + 4) % 7;
+
+    /* Year */
+    year = 1970;
+    while (seconds >= LEAP_YEAR_SECONDS)
+    {
+        if (is_leapyear(year)){
+            seconds -= LEAP_YEAR_SECONDS;
+        } else {
+            seconds -= YEAR_SECONDS;
+        }
+
+        year++;
+    }
+
+    if (is_leapyear(year)) {
+        days_in_month[1] = 29;
+    } else {
+        days_in_month[1] = 28;
+        if(seconds>YEAR_SECONDS){
+            year++;
+            seconds -= YEAR_SECONDS;
+        }
+    }
+    tm->tm_year = year%100 + 100;
+
+    /* Month */
+    for (i = 0; i < 12; i++)
+    {
+        if (seconds < days_in_month[i]*DAY_SECONDS){
+            tm->tm_mon = i;
+            break;
+        }
+
+        seconds -= days_in_month[i]*DAY_SECONDS;
+    }
+
+    /* Month Day */
+    mday = seconds/DAY_SECONDS;
+    seconds -= mday*DAY_SECONDS;
+    tm->tm_mday = mday + 1; /* 1 ... 31 */
+
+    /* Hour */
+    hour = seconds/HOUR_SECONDS;
+    seconds -= hour*HOUR_SECONDS;
+    tm->tm_hour = hour;
+
+    /* Minute */
+    min = seconds/MINUTE_SECONDS;
+    seconds -= min*MINUTE_SECONDS;
+    tm->tm_min = min;
+
+    /* Second */
+    tm->tm_sec = seconds;
+
+    return tm;
+}
+

firmware/libc/include/time.h

@@ -34,6 +34,8 @@ typedef long time_t;
 #define _TIME_T_DECLARED
 time_t time(time_t *t);
 struct tm *localtime(const time_t *timep);
+struct tm *gmtime(const time_t *timep);
+struct tm *gmtime_r(const time_t *timep, struct tm *result);
 time_t mktime(struct tm *t);
 
 #endif /* SIMULATOR */