--- /dev/null
+/*
+
+Copyright (c) 2007-2008 Michael G Schwern
+
+This software originally derived from Paul Sheer's pivotal_gmtime_r.c.
+
+The MIT License:
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+
+*/
+
+/* See http://code.google.com/p/y2038 for this code's origin */
+
+#include <assert.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+#include <errno.h>
+
+/* Spec says except for stftime() and the _r() functions, these
+ all return static memory. Stabbings! */
+static struct tm Static_Return_Date;
+static char Static_Return_String[35];
+
+static const int days_in_month[2][12] = {
+ {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
+ {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
+};
+
+static const int julian_days_by_month[2][12] = {
+ {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334},
+ {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335},
+};
+
+static char const wday_name[7][3] = {
+ "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
+};
+
+static char const mon_name[12][3] = {
+ "Jan", "Feb", "Mar", "Apr", "May", "Jun",
+ "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
+};
+
+static const int length_of_year[2] = { 365, 366 };
+
+/* Some numbers relating to the gregorian cycle */
+static const int64_t years_in_gregorian_cycle = 400;
+#define days_in_gregorian_cycle ((365 * 400) + 100 - 4 + 1)
+static const int64_t seconds_in_gregorian_cycle = days_in_gregorian_cycle * 60LL * 60LL * 24LL;
+
+/* Year range we can trust the time funcitons with */
+#define MAX_SAFE_YEAR 2037
+#define MIN_SAFE_YEAR 1971
+
+/* 28 year Julian calendar cycle */
+#define SOLAR_CYCLE_LENGTH 28
+
+/* Year cycle from MAX_SAFE_YEAR down. */
+static const int safe_years_high[SOLAR_CYCLE_LENGTH] = {
+ 2016, 2017, 2018, 2019,
+ 2020, 2021, 2022, 2023,
+ 2024, 2025, 2026, 2027,
+ 2028, 2029, 2030, 2031,
+ 2032, 2033, 2034, 2035,
+ 2036, 2037, 2010, 2011,
+ 2012, 2013, 2014, 2015
+};
+
+/* Year cycle from MIN_SAFE_YEAR up */
+static const int safe_years_low[SOLAR_CYCLE_LENGTH] = {
+ 1996, 1997, 1998, 1971,
+ 1972, 1973, 1974, 1975,
+ 1976, 1977, 1978, 1979,
+ 1980, 1981, 1982, 1983,
+ 1984, 1985, 1986, 1987,
+ 1988, 1989, 1990, 1991,
+ 1992, 1993, 1994, 1995,
+};
+
+/* Let's assume people are going to be looking for dates in the future.
+ Let's provide some cheats so you can skip ahead.
+ This has a 4x speed boost when near 2008.
+*/
+/* Number of days since epoch on Jan 1st, 2008 GMT */
+#define CHEAT_DAYS (1199145600 / 24 / 60 / 60)
+#define CHEAT_YEARS 108
+
+#define IS_LEAP(n) ((!(((n) + 1900) % 400) || (!(((n) + 1900) % 4) && (((n) + 1900) % 100))) != 0)
+#define WRAP(a,b,m) ((a) = ((a) < 0 ) ? ((b)--, (a) + (m)) : (a))
+
+/* timegm() is not in the C or POSIX spec, but it is such a useful
+ extension I would be remiss in leaving it out. Also I need it
+ for localtime64()
+*/
+int64_t btls_timegm64(const struct tm *date) {
+ int64_t days = 0;
+ int64_t seconds = 0;
+ int64_t year;
+ int64_t orig_year = (int64_t)date->tm_year;
+ int cycles = 0;
+
+ if( orig_year > 100 ) {
+ cycles = (orig_year - 100) / 400;
+ orig_year -= cycles * 400;
+ days += (int64_t)cycles * days_in_gregorian_cycle;
+ }
+ else if( orig_year < -300 ) {
+ cycles = (orig_year - 100) / 400;
+ orig_year -= cycles * 400;
+ days += (int64_t)cycles * days_in_gregorian_cycle;
+ }
+
+ if( orig_year > 70 ) {
+ year = 70;
+ while( year < orig_year ) {
+ days += length_of_year[IS_LEAP(year)];
+ year++;
+ }
+ }
+ else if ( orig_year < 70 ) {
+ year = 69;
+ do {
+ days -= length_of_year[IS_LEAP(year)];
+ year--;
+ } while( year >= orig_year );
+ }
+
+
+ days += julian_days_by_month[IS_LEAP(orig_year)][date->tm_mon];
+ days += date->tm_mday - 1;
+
+ seconds = days * 60 * 60 * 24;
+
+ seconds += date->tm_hour * 60 * 60;
+ seconds += date->tm_min * 60;
+ seconds += date->tm_sec;
+
+ return(seconds);
+}
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