1 files changed, 113 insertions, 0 deletions
diff --git a/time/mk_gmtime.c b/time/mk_gmtime.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: mk_gmtime.c 2369 2013-04-28 14:19:35Z swfltek $ */
+
+/*
+    'Break down' a y2k time stamp into the elements of struct tm.
+    Unlike mktime(), this function does not 'normalize' the elements of timeptr.
+
+*/
+
+#include <time.h>
+
+time_t
+mk_gmtime(const struct tm * timeptr)
+{
+
+    time_t          ret;
+    uint32_t        tmp;
+    int             n, m, d, leaps;
+
+    /*
+        Determine elapsed whole days since the epoch to the beginning of this year. Since our epoch is
+        at a conjunction of the leap cycles, we can do this rather quickly.
+        */
+    n = timeptr->tm_year - 100;
+    leaps = 0;
+    if (n) {
+        m = n - 1;
+        leaps = m / 4;
+        leaps -= m / 100;
+        leaps++;
+    }
+    tmp = 365UL * n + leaps;
+
+    /*
+                Derive the day of year from month and day of month. We use the pattern of 31 day months
+                followed by 30 day months to our advantage, but we must 'special case' Jan/Feb, and
+                account for a 'phase change' between July and August (153 days after March 1).
+            */
+    d = timeptr->tm_mday - 1;   /* tm_mday is one based */
+
+    /* handle Jan/Feb as a special case */
+    if (timeptr->tm_mon < 2) {
+        if (timeptr->tm_mon)
+            d += 31;
+
+    } else {
+        n = 59 + is_leap_year(timeptr->tm_year + 1900);
+        d += n;
+        n = timeptr->tm_mon - MARCH;
+
+        /* account for phase change */
+        if (n > (JULY - MARCH))
+            d += 153;
+        n %= 5;
+
+        /*
+         * n is now an index into a group of alternating 31 and 30
+         * day months... 61 day pairs.
+         */
+        m = n / 2;
+        m *= 61;
+        d += m;
+
+        /*
+         * if n is odd, we are in the second half of the
+         * month pair
+         */
+        if (n & 1)
+            d += 31;
+    }
+
+    /* Add day of year to elapsed days, and convert to seconds */
+    tmp += d;
+    tmp *= ONE_DAY;
+    ret = tmp;
+
+    /* compute 'fractional' day */
+    tmp = timeptr->tm_hour;
+    tmp *= ONE_HOUR;
+    tmp += timeptr->tm_min * 60UL;
+    tmp += timeptr->tm_sec;
+
+    ret += tmp;
+
+    return ret;
+}