switch to avr-libc 1.8.1 time library

[z180-stamp.git] / time / gmtime_r.c

diff --git a/time/gmtime_r.c b/time/gmtime_r.c
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+/*
+ * (C)2012 Michael Duane Rice All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * Redistributions of source code must retain the above copyright notice, this
+ * list of conditions and the following disclaimer. Redistributions in binary
+ * form must reproduce the above copyright notice, this list of conditions
+ * and the following disclaimer in the documentation and/or other materials
+ * provided with the distribution. Neither the name of the copyright holders
+ * nor the names of contributors may be used to endorse or promote products
+ * derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/* $Id: gmtime_r.c 2369 2013-04-28 14:19:35Z swfltek $ */
+
+/* Re entrant version of gmtime(). */
+
+#include <time.h>
+#include <stdlib.h>
+#include <inttypes.h>
+
+void
+gmtime_r(const time_t * timer, struct tm * timeptr)
+{
+    int32_t         fract;
+    ldiv_t          lresult;
+    div_t           result;
+    uint16_t        days, n, leapyear, years;
+
+    /* break down timer into whole and fractional parts of 1 day */
+    days = *timer / 86400UL;
+    fract = *timer % 86400UL;
+
+    /*
+            Extract hour, minute, and second from the fractional day
+        */
+    lresult = ldiv(fract, 60L);
+    timeptr->tm_sec = lresult.rem;
+    result = div(lresult.quot, 60);
+    timeptr->tm_min = result.rem;
+    timeptr->tm_hour = result.quot;
+
+    /* Determine day of week ( the epoch was a Saturday ) */
+    n = days + SATURDAY;
+    n %= 7;
+    timeptr->tm_wday = n;
+
+    /*
+        * Our epoch year has the property of being at the conjunction of all three 'leap cycles',
+        * 4, 100, and 400 years ( though we can ignore the 400 year cycle in this library).
+        *
+        * Using this property, we can easily 'map' the time stamp into the leap cycles, quickly
+        * deriving the year and day of year, along with the fact of whether it is a leap year.
+        */
+
+    /* map into a 100 year cycle */
+    lresult = ldiv((long) days, 36525L);
+    years = 100 * lresult.quot;
+
+    /* map into a 4 year cycle */
+    lresult = ldiv(lresult.rem, 1461L);
+    years += 4 * lresult.quot;
+    days = lresult.rem;
+    if (years > 100)
+        days++;
+
+    /*
+         * 'years' is now at the first year of a 4 year leap cycle, which will always be a leap year,
+         * unless it is 100. 'days' is now an index into that cycle.
+         */
+    leapyear = 1;
+    if (years == 100)
+        leapyear = 0;
+
+    /* compute length, in days, of first year of this cycle */
+    n = 364 + leapyear;
+
+    /*
+     * if the number of days remaining is greater than the length of the
+     * first year, we make one more division.
+     */
+    if (days > n) {
+        days -= leapyear;
+        leapyear = 0;
+        result = div(days, 365);
+        years += result.quot;
+        days = result.rem;
+    }
+    timeptr->tm_year = 100 + years;
+    timeptr->tm_yday = days;
+
+    /*
+            Given the year, day of year, and leap year indicator, we can break down the
+            month and day of month. If the day of year is less than 59 (or 60 if a leap year), then
+            we handle the Jan/Feb month pair as an exception.
+        */
+    n = 59 + leapyear;
+    if (days < n) {
+        /* special case: Jan/Feb month pair */
+        result = div(days, 31);
+        timeptr->tm_mon = result.quot;
+        timeptr->tm_mday = result.rem;
+    } else {
+        /*
+            The remaining 10 months form a regular pattern of 31 day months alternating with 30 day
+            months, with a 'phase change' between July and August (153 days after March 1).
+            We proceed by mapping our position into either March-July or August-December.
+            */
+        days -= n;
+        result = div(days, 153);
+        timeptr->tm_mon = 2 + result.quot * 5;
+
+        /* map into a 61 day pair of months */
+        result = div(result.rem, 61);
+        timeptr->tm_mon += result.quot * 2;
+
+        /* map into a month */
+        result = div(result.rem, 31);
+        timeptr->tm_mon += result.quot;
+        timeptr->tm_mday = result.rem;
+    }
+
+    /*
+            Cleanup and return
+        */
+    timeptr->tm_isdst = 0;  /* gmt is never in DST */
+    timeptr->tm_mday++; /* tm_mday is 1 based */
+
+}