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Diffstat (limited to 'time/gmtime_r.c')
| -rw-r--r-- | time/gmtime_r.c | 144 |
1 files changed, 144 insertions, 0 deletions
diff --git a/time/gmtime_r.c b/time/gmtime_r.c new file mode 100644 index 0000000..22658ea --- /dev/null +++ b/time/gmtime_r.c @@ -0,0 +1,144 @@ +/* + * (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 */ + +} |