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[PATCH] 2038 fix



Attached is the latest 2038 patch from the y2038 branch.

* Configure now probes for the safe range of the system's
  localtime() and gmtime().  Perl will use the system
  functions inside their safe range.  [Thanks Merijn]

* Perl now ships with its own 64 bit gmtime() and timegm().

* localtime() is made 2038 safe on 32 bit systems using the algorithm
  described here
  http://code.google.com/p/y2038/wiki/HowItWorks

* Time::Local can now handle past 2038.

* Time::gmtime tests improved and expanded past 2038 and 1901.

* Time::localtime tests improved and expanded past 2038.


Open issues

* localtime64.h and .c need to be wired into the Makefile.
  I don't now how to do this.

* The LOCALTIME_EDGECASE_BROKEN special case needs to be
  reincorporated.

* This has not been tested on a system with an unsigned or floating point
  time_t.

* The configure probes are probably broken with a floating point time_t.


Other notes

* The clever way Time::Local handles the year (8, 108 and 2008 are all 2008)
  means there are gaps in what years you can run through timelocal() and
  timegm().

* Since localtime64.c now has its own timegm() core time modules could
  make use of it.


I've hit the limit of what I can do alone.  I'd like to see this incorporated
into the bleadperl trunk so it can get some cross-platform testing.


-- 
s7ank: i want to be one of those guys that types "s/j&jd//.^$ueu*///djsls/sm."
       and it's a perl script that turns dog crap into gold.

diff --git a/.gitignore b/.gitignore
index 40e7eb2..9d7069b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,6 +24,7 @@
 # general build products
 *.o
 *.a
+*.old
 
 # ?
 ext.libs
diff --git a/lib/Time/Local.pm b/lib/Time/Local.pm
index 4044cd9..e5c4f88 100644
--- a/lib/Time/Local.pm
+++ b/lib/Time/Local.pm
@@ -4,7 +4,6 @@ require Exporter;
 use Carp;
 use Config;
 use strict;
-use integer;
 
 use vars qw( $VERSION @ISA @EXPORT @EXPORT_OK );
 $VERSION   = '1.18_01';
@@ -29,13 +28,8 @@ use constant SECS_PER_MINUTE => 60;
 use constant SECS_PER_HOUR   => 3600;
 use constant SECS_PER_DAY    => 86400;
 
-my $MaxInt = ( ( 1 << ( 8 * $Config{ivsize} - 2 ) ) - 1 ) * 2 + 1;
-my $MaxDay = int( ( $MaxInt - ( SECS_PER_DAY / 2 ) ) / SECS_PER_DAY ) - 1;
-
-if ( $^O eq 'MacOS' ) {
-    # time_t is unsigned...
-    $MaxInt = ( 1 << ( 8 * $Config{ivsize} ) ) - 1;
-}
+# localtime()'s limit is the year 2**31
+my $MaxDay = 365 * (2**31);
 
 # Determine the EPOC day for this machine
 my $Epoc = 0;
@@ -65,13 +59,13 @@ sub _daygm {
     return $_[3] + (
         $Cheat{ pack( 'ss', @_[ 4, 5 ] ) } ||= do {
             my $month = ( $_[4] + 10 ) % 12;
-            my $year  = $_[5] + 1900 - $month / 10;
+            my $year  = $_[5] + 1900 - int($month / 10);
 
             ( ( 365 * $year )
-              + ( $year / 4 )
-              - ( $year / 100 )
-              + ( $year / 400 )
-              + ( ( ( $month * 306 ) + 5 ) / 10 )
+              + int( $year / 4 )
+              - int( $year / 100 )
+              + int( $year / 400 )
+              + int( ( ( $month * 306 ) + 5 ) / 10 )
             )
             - $Epoc;
         }
@@ -278,16 +272,6 @@ absolute four digit year instead.
 The scheme above allows interpretation of a wide range of dates,
 particularly if 4-digit years are used.
 
-=head2 Limits of time_t
-
-The range of dates that can be actually be handled depends on the size
-of C<time_t> (usually a signed integer) on the given
-platform. Currently, this is 32 bits for most systems, yielding an
-approximate range from Dec 1901 to Jan 2038.
-
-Both C<timelocal()> and C<timegm()> croak if given dates outside the
-supported range.
-
 =head2 Ambiguous Local Times (DST)
 
 Because of DST changes, there are many time zones where the same local
@@ -310,17 +294,6 @@ for the "Europe/Paris" time zone, the local clock jumped from
 If the C<timelocal()> function is given a non-existent local time, it
 will simply return an epoch value for the time one hour later.
 
-=head2 Negative Epoch Values
-
-Negative epoch (C<time_t>) values are not officially supported by the
-POSIX standards, so this module's tests do not test them. On some
-systems, they are known not to work. These include MacOS (pre-OSX) and
-Win32.
-
-On systems which do support negative epoch values, this module should
-be able to cope with dates before the start of the epoch, down the
-minimum value of time_t for the system.
-
 =head1 IMPLEMENTATION
 
 These routines are quite efficient and yet are always guaranteed to
diff --git a/lib/Time/Local.t b/lib/Time/Local.t
index 22138cf..ef32b40 100755
--- a/lib/Time/Local.t
+++ b/lib/Time/Local.t
@@ -25,10 +25,10 @@ my @time =
    # leap day
    [2020,  2, 29, 12, 59, 59],
    [2030,  7,  4, 17, 07, 06],
-# The following test fails on a surprising number of systems
-# so it is commented out. The end of the Epoch for a 32-bit signed
-# implementation of time_t should be Jan 19, 2038  03:14:07 UTC.
-#  [2038,  1, 17, 23, 59, 59],     # last full day in any tz
+   [2038,  1, 17, 23, 59, 59],     # last full day in any tz
+
+   # more than 2**31 time_t
+   [2258,  8, 11,  1, 49, 17],
   );
 
 my @bad_time =
@@ -88,7 +88,7 @@ for (@time, @neg_time) {
     $year -= 1900;
     $mon--;
 
- SKIP: {
+    SKIP: {
         skip '1970 test on VOS fails.', 12
             if $^O eq 'vos' && $year == 70;
         skip 'this platform does not support negative epochs.', 12
@@ -107,20 +107,21 @@ for (@time, @neg_time) {
             is($M, $mon, "timelocal month for @$_");
             is($Y, $year, "timelocal year for @$_");
         }
+    }
 
-        {
-            my $year_in = $year < 70 ? $year + 1900 : $year;
-            my $time = timegm($sec,$min,$hour,$mday,$mon,$year_in);
+    # Perl has its own gmtime()
+    {
+        my $year_in = $year < 70 ? $year + 1900 : $year;
+        my $time = timegm($sec,$min,$hour,$mday,$mon,$year_in);
 
-            my($s,$m,$h,$D,$M,$Y) = gmtime($time);
+        my($s,$m,$h,$D,$M,$Y) = gmtime($time);
 
-            is($s, $sec, "timegm second for @$_");
-            is($m, $min, "timegm minute for @$_");
-            is($h, $hour, "timegm hour for @$_");
-            is($D, $mday, "timegm day for @$_");
-            is($M, $mon, "timegm month for @$_");
-            is($Y, $year, "timegm year for @$_");
-        }
+        is($s, $sec, "timegm second for @$_");
+        is($m, $min, "timegm minute for @$_");
+        is($h, $hour, "timegm hour for @$_");
+        is($D, $mday, "timegm day for @$_");
+        is($M, $mon, "timegm month for @$_");
+        is($Y, $year, "timegm year for @$_");
     }
 }
 
@@ -166,11 +167,7 @@ for my $p (@years) {
         "$year $string a leap year" );
 }
 
-SKIP:
 {
-    skip 'this platform does not support negative epochs.', 6
-        unless $neg_epoch_ok;
-
     eval { timegm(0,0,0,29,1,1900) };
     like($@, qr/Day '29' out of range 1\.\.28/,
          'does not accept leap day in 1900');
diff --git a/lib/Time/gmtime.t b/lib/Time/gmtime.t
index 853ec3b..1ccd7fb 100644
--- a/lib/Time/gmtime.t
+++ b/lib/Time/gmtime.t
@@ -3,55 +3,26 @@
 BEGIN {
     chdir 't' if -d 't';
     @INC = '../lib';
-}
 
-BEGIN {
-    our $hasgm;
-    eval { my $n = gmtime 0 };
-    $hasgm = 1 unless $@ && $@ =~ /unimplemented/;
-    unless ($hasgm) { print "1..0 # Skip: no gmtime\n"; exit 0 }
+    require "./test.pl";
 }
 
+my(@times, @methods);
 BEGIN {
-    our @gmtime = gmtime 0; # This is the function gmtime.
-    unless (@gmtime) { print "1..0 # Skip: gmtime failed\n"; exit 0 }
-}
-
-print "1..10\n";
-
-use Time::gmtime;
-
-print "ok 1\n";
-
-my $gmtime = gmtime 0 ; # This is the OO gmtime.
-
-print "not " unless $gmtime->sec   == $gmtime[0];
-print "ok 2\n";
-
-print "not " unless $gmtime->min   == $gmtime[1];
-print "ok 3\n";
-
-print "not " unless $gmtime->hour  == $gmtime[2];
-print "ok 4\n";
-
-print "not " unless $gmtime->mday  == $gmtime[3];
-print "ok 5\n";
-
-print "not " unless $gmtime->mon   == $gmtime[4];
-print "ok 6\n";
-
-print "not " unless $gmtime->year  == $gmtime[5];
-print "ok 7\n";
-
-print "not " unless $gmtime->wday  == $gmtime[6];
-print "ok 8\n";
-
-print "not " unless $gmtime->yday  == $gmtime[7];
-print "ok 9\n";
-
-print "not " unless $gmtime->isdst == $gmtime[8];
-print "ok 10\n";
+    @times   = (-2**33, -2**31-1, 0, 2**31-1, 2**33, time);
+    @methods = qw(sec min hour mday mon year wday yday isdst);
 
+    plan tests => (@times * @methods) + 1;
 
+    use_ok Time::gmtime;
+}
 
+# Perl has its own gmtime() so it's safe to do negative times.
+for my $time (@times) {
+    my $gmtime = gmtime $time;          # This is the OO gmtime.
+    my @gmtime = CORE::gmtime $time;    # This is the gmtime function
 
+    for my $method (@methods) {
+        is $gmtime->$method, shift @gmtime, "gmtime($time)->$method";
+    }
+}
diff --git a/lib/Time/localtime.t b/lib/Time/localtime.t
index 357615c..10df765 100644
--- a/lib/Time/localtime.t
+++ b/lib/Time/localtime.t
@@ -3,55 +3,35 @@
 BEGIN {
     chdir 't' if -d 't';
     @INC = '../lib';
+
+    require "./test.pl";
 }
 
 BEGIN {
-    our $haslocal;
+    my $haslocal;
     eval { my $n = localtime 0 };
     $haslocal = 1 unless $@ && $@ =~ /unimplemented/;
-    unless ($haslocal) { print "1..0 # Skip: no localtime\n"; exit 0 }
-}
 
-BEGIN {
-    our @localtime = localtime 0; # This is the function localtime.
-    unless (@localtime) { print "1..0 # Skip: localtime failed\n"; exit 0 }
+    skip_all("no localtime") unless $haslocal;
 }
 
-print "1..10\n";
-
-use Time::localtime;
-
-print "ok 1\n";
-
-my $localtime = localtime 0 ; # This is the OO localtime.
-
-print "not " unless $localtime->sec   == $localtime[0];
-print "ok 2\n";
-
-print "not " unless $localtime->min   == $localtime[1];
-print "ok 3\n";
-
-print "not " unless $localtime->hour  == $localtime[2];
-print "ok 4\n";
-
-print "not " unless $localtime->mday  == $localtime[3];
-print "ok 5\n";
-
-print "not " unless $localtime->mon   == $localtime[4];
-print "ok 6\n";
-
-print "not " unless $localtime->year  == $localtime[5];
-print "ok 7\n";
-
-print "not " unless $localtime->wday  == $localtime[6];
-print "ok 8\n";
-
-print "not " unless $localtime->yday  == $localtime[7];
-print "ok 9\n";
+BEGIN {
+    my @localtime = CORE::localtime 0; # This is the function localtime.
 
-print "not " unless $localtime->isdst == $localtime[8];
-print "ok 10\n";
+    skip_all("localtime failed") unless @localtime;
+}
 
+BEGIN { plan tests => 37; }
 
+BEGIN { use_ok Time::localtime; }
 
+# Since Perl's localtime() still uses the system localtime, don't try
+# to do negative times.  The system might not support it.
+for my $time (0, 2**31-1, 2**33, time) {
+    my $localtime = localtime $time;          # This is the OO localtime.
+    my @localtime = CORE::localtime $time;    # This is the localtime function
 
+    for my $method (qw(sec min hour mday mon year wday yday isdst)) {
+        is $localtime->$method, shift @localtime, "localtime($time)->$method";
+    }
+}
diff --git a/localtime64.c b/localtime64.c
new file mode 100644
index 0000000..0c54bc3
--- /dev/null
+++ b/localtime64.c
@@ -0,0 +1,438 @@
+/* 
+
+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.
+
+*/
+
+/*
+
+Programmers who have available to them 64-bit time values as a 'long
+long' type can use localtime64_r() and gmtime64_r() which correctly
+converts the time even on 32-bit systems. Whether you have 64-bit time 
+values will depend on the operating system.
+
+localtime64_r() is a 64-bit equivalent of localtime_r().
+
+gmtime64_r() is a 64-bit equivalent of gmtime_r().
+
+*/
+
+#include "localtime64.h"
+
+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 const int length_of_year[2] = { 365, 366 };
+
+/* Number of days in a 400 year Gregorian cycle */
+static const int years_in_gregorian_cycle = 400;
+static const int days_in_gregorian_cycle  = (365 * 400) + 100 - 4 + 1;
+
+/* 28 year calendar cycle between 2010 and 2037 */
+static const int safe_years[28] = {
+    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
+};
+
+#define SOLAR_CYCLE_LENGTH 28
+static const int dow_year_start[SOLAR_CYCLE_LENGTH] = {
+    5, 0, 1, 2,     /* 0       2016 - 2019 */
+    3, 5, 6, 0,     /* 4  */
+    1, 3, 4, 5,     /* 8  */
+    6, 1, 2, 3,     /* 12 */
+    4, 6, 0, 1,     /* 16 */
+    2, 4, 5, 6,     /* 20      2036, 2037, 2010, 2011 */
+    0, 2, 3, 4      /* 24      2012, 2013, 2014, 2015 */
+};
+
+/* 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))
+
+#define SHOULD_USE_SYSTEM_LOCALTIME(a)  (       \
+    USE_SYSTEM_LOCALTIME        &&              \
+    (a) <= SYSTEM_LOCALTIME_MAX &&              \
+    (a) >= SYSTEM_LOCALTIME_MIN                 \
+)
+#define SHOULD_USE_SYSTEM_GMTIME(a)     (       \
+    USE_SYSTEM_GMTIME           &&              \
+    (a) <= SYSTEM_GMTIME_MAX    &&              \
+    (a) >= SYSTEM_GMTIME_MIN                    \
+)
+
+
+int _is_exception_century(Int64 year)
+{
+    int is_exception = ((year % 100 == 0) && !(year % 400 == 0));
+    /* printf("is_exception_century: %s\n", is_exception ? "yes" : "no"); */
+
+    return(is_exception);
+}
+
+
+/* timegm() is a GNU extension, so emulate it here if we need it */
+#ifdef HAS_TIMEGM
+#    define TIMEGM(n) timegm(n);
+#else
+#    define TIMEGM(n) ((time_t)timegm64(n));
+#endif
+
+Time64_T timegm64(struct tm *date) {
+    int   days    = 0;
+    Int64 seconds = 0;
+    Int64 year;
+
+    if( date->tm_year > 70 ) {
+        year = 70;
+        while( year < date->tm_year ) {
+            days += length_of_year[IS_LEAP(year)];
+            year++;
+        }
+    }
+    else if ( date->tm_year < 70 ) {
+        year = 69;
+        do {
+            days -= length_of_year[IS_LEAP(year)];
+            year--;
+        } while( year >= date->tm_year );
+    }
+
+    days += julian_days_by_month[IS_LEAP(date->tm_year)][date->tm_mon];
+    days += date->tm_mday - 1;
+
+    /* Avoid overflowing the days integer */
+    seconds = days;
+    seconds = seconds * 60 * 60 * 24;
+
+    seconds += date->tm_hour * 60 * 60;
+    seconds += date->tm_min * 60;
+    seconds += date->tm_sec;
+
+    return((Time64_T)seconds);
+}
+
+
+int _check_tm(struct tm *tm)
+{
+    /* Don't forget leap seconds */
+    assert(tm->tm_sec >= 0);
+    assert(tm->tm_sec <= 61);
+
+    assert(tm->tm_min >= 0);
+    assert(tm->tm_min <= 59);
+
+    assert(tm->tm_hour >= 0);
+    assert(tm->tm_hour <= 23);
+
+    assert(tm->tm_mday >= 1);
+    assert(tm->tm_mday <= days_in_month[IS_LEAP(tm->tm_year)][tm->tm_mon]);
+
+    assert(tm->tm_mon  >= 0);
+    assert(tm->tm_mon  <= 11);
+
+    assert(tm->tm_wday >= 0);
+    assert(tm->tm_wday <= 6);
+    
+    assert(tm->tm_yday >= 0);
+    assert(tm->tm_yday <= length_of_year[IS_LEAP(tm->tm_year)]);
+
+#ifdef HAS_TM_TM_GMTOFF
+    assert(tm->tm_gmtoff >= -24 * 60 * 60);
+    assert(tm->tm_gmtoff <=  24 * 60 * 60);
+#endif
+
+    return 1;
+}
+
+
+/* The exceptional centuries without leap years cause the cycle to
+   shift by 16
+*/
+int _cycle_offset(Int64 year)
+{
+    const Int64 start_year = 2000;
+    Int64 year_diff  = year - start_year;
+
+    if( year > start_year )
+        year_diff--;
+
+    Int64 exceptions  = year_diff / 100;
+    exceptions       -= year_diff / 400;
+
+    /*
+    fprintf(stderr, "# year: %lld, exceptions: %lld, year_diff: %lld\n",
+            year, exceptions, year_diff);
+    */
+
+    return exceptions * 16;
+}
+
+/* For a given year after 2038, pick the latest possible matching
+   year in the 28 year calendar cycle.
+
+   A matching year...
+   1) Starts on the same day of the week.
+   2) Has the same leap year status.
+
+   This is so the calendars match up.
+
+   Also the previous year must match.  When doing Jan 1st you might
+   wind up on Dec 31st the previous year when doing a -UTC time zone.
+
+   Finally, the next year must have the same start day of week.  This
+   is for Dec 31st with a +UTC time zone.
+   It doesn't need the same leap year status since we only care about
+   January 1st.
+*/
+int _safe_year(Int64 year)
+{
+    int safe_year;
+    Int64 year_cycle = year + _cycle_offset(year);
+
+    /* Change non-leap xx00 years to an equivalent */
+    if( _is_exception_century(year) )
+        year_cycle += 11;
+
+    /* Also xx01 years, since the previous year will be wrong */
+    if( _is_exception_century(year - 1) )
+        year_cycle += 17;
+
+    year_cycle %= SOLAR_CYCLE_LENGTH;
+    if( year_cycle < 0 ) 
+        year_cycle = SOLAR_CYCLE_LENGTH + year_cycle;
+
+    assert( year_cycle >= 0 );
+    assert( year_cycle < SOLAR_CYCLE_LENGTH );
+    safe_year = safe_years[year_cycle];
+
+    assert(safe_year <= 2037 && safe_year >= 2010);
+    
+    /*
+    printf("year: %d, year_cycle: %d, safe_year: %d\n",
+           year, year_cycle, safe_year);
+    */
+
+    return safe_year;
+}
+
+struct tm *gmtime64_r (const Time64_T *in_time, struct tm *p)
+{
+    int v_tm_sec, v_tm_min, v_tm_hour, v_tm_mon, v_tm_wday;
+    Int64 v_tm_tday;
+    int leap;
+    Int64 m;
+    Time64_T time = *in_time;
+    Int64 year = 70;
+
+    /* Use the system gmtime() if time_t is small enough */
+    if( SHOULD_USE_SYSTEM_GMTIME(*in_time) ) {
+        time_t safe_time = *in_time;
+        localtime_r(&safe_time, p);
+        assert(_check_tm(p));
+        return p;
+    }
+
+#ifdef HAS_TM_TM_GMTOFF
+    p->tm_gmtoff = 0;
+#endif
+    p->tm_isdst  = 0;
+
+#ifdef HAS_TM_TM_ZONE
+    p->tm_zone   = "UTC";
+#endif
+
+    v_tm_sec =  time % 60;
+    time /= 60;
+    v_tm_min =  time % 60;
+    time /= 60;
+    v_tm_hour = time % 24;
+    time /= 24;
+    v_tm_tday = time;
+    WRAP (v_tm_sec, v_tm_min, 60);
+    WRAP (v_tm_min, v_tm_hour, 60);
+    WRAP (v_tm_hour, v_tm_tday, 24);
+    if ((v_tm_wday = (v_tm_tday + 4) % 7) < 0)
+        v_tm_wday += 7;
+    m = v_tm_tday;
+
+    if (m >= CHEAT_DAYS) {
+        year = CHEAT_YEARS;
+        m -= CHEAT_DAYS;
+    }
+
+    if (m >= 0) {
+        /* Gregorian cycles, this is huge optimization for distant times */
+        while (m >= (Time64_T) days_in_gregorian_cycle) {
+            m -= (Time64_T) days_in_gregorian_cycle;
+            year += years_in_gregorian_cycle;
+        }
+
+        /* Years */
+        leap = IS_LEAP (year);
+        while (m >= (Time64_T) length_of_year[leap]) {
+            m -= (Time64_T) length_of_year[leap];
+            year++;
+            leap = IS_LEAP (year);
+        }
+
+        /* Months */
+        v_tm_mon = 0;
+        while (m >= (Time64_T) days_in_month[leap][v_tm_mon]) {
+            m -= (Time64_T) days_in_month[leap][v_tm_mon];
+            v_tm_mon++;
+        }
+    } else {
+        year--;
+
+        /* Gregorian cycles */
+        while (m < (Time64_T) -days_in_gregorian_cycle) {
+            m += (Time64_T) days_in_gregorian_cycle;
+            year -= years_in_gregorian_cycle;
+        }
+
+        /* Years */
+        leap = IS_LEAP (year);
+        while (m < (Time64_T) -length_of_year[leap]) {
+            m += (Time64_T) length_of_year[leap];
+            year--;
+            leap = IS_LEAP (year);
+        }
+
+        /* Months */
+        v_tm_mon = 11;
+        while (m < (Time64_T) -days_in_month[leap][v_tm_mon]) {
+            m += (Time64_T) days_in_month[leap][v_tm_mon];
+            v_tm_mon--;
+        }
+        m += (Time64_T) days_in_month[leap][v_tm_mon];
+    }
+
+    p->tm_year = year;
+    if( p->tm_year != year ) {
+#ifdef EOVERFLOW
+        errno = EOVERFLOW;
+#endif
+        return NULL;
+    }
+
+    p->tm_mday = (int) m + 1;
+    p->tm_yday = julian_days_by_month[leap][v_tm_mon] + m;
+    p->tm_sec = v_tm_sec, p->tm_min = v_tm_min, p->tm_hour = v_tm_hour,
+        p->tm_mon = v_tm_mon, p->tm_wday = v_tm_wday;
+    
+    assert(_check_tm(p));
+
+    return p;
+}
+
+
+struct tm *localtime64_r (const Time64_T *time, struct tm *local_tm)
+{
+    time_t safe_time;
+    struct tm gm_tm;
+    Int64 orig_year;
+    int month_diff;
+
+    /* Use the system localtime() if time_t is small enough */
+    if( SHOULD_USE_SYSTEM_LOCALTIME(*time) ) {
+        safe_time = *time;
+        localtime_r(&safe_time, local_tm);
+        assert(_check_tm(local_tm));
+        return local_tm;
+    }
+
+    if( gmtime64_r(time, &gm_tm) == NULL )
+        return NULL;
+
+    orig_year = gm_tm.tm_year;
+
+    if (gm_tm.tm_year > (2037 - 1900) ||
+        gm_tm.tm_year < (1902 - 1900)
+       )
+    {
+        gm_tm.tm_year = _safe_year(gm_tm.tm_year + 1900) - 1900;
+    }
+
+    safe_time = TIMEGM(&gm_tm);
+    if( localtime_r(&safe_time, local_tm) == NULL )
+        return NULL;
+
+    local_tm->tm_year = orig_year;
+    if( local_tm->tm_year != orig_year ) {
+#ifdef EOVERFLOW
+        errno = EOVERFLOW;
+#endif
+        return NULL;
+    }
+
+
+    month_diff = local_tm->tm_mon - gm_tm.tm_mon;
+
+    /*  When localtime is Dec 31st previous year and
+        gmtime is Jan 1st next year.
+    */
+    if( month_diff == 11 ) {
+        local_tm->tm_year--;
+    }
+
+    /*  When localtime is Jan 1st, next year and
+        gmtime is Dec 31st, previous year.
+    */
+    if( month_diff == -11 ) {
+        local_tm->tm_year++;
+    }
+
+    /* GMT is Jan 1st, xx01 year, but localtime is still Dec 31st 
+       in a non-leap xx00.  There is one point in the cycle
+       we can't account for which the safe xx00 year is a leap
+       year.  So we need to correct for Dec 31st comming out as
+       the 366th day of the year.
+    */
+    if( !IS_LEAP(local_tm->tm_year) && local_tm->tm_yday == 365 )
+        local_tm->tm_yday--;
+
+    assert(_check_tm(local_tm));
+    
+    return local_tm;
+}
diff --git a/localtime64.h b/localtime64.h
new file mode 100644
index 0000000..b7bd00e
--- /dev/null
+++ b/localtime64.h
@@ -0,0 +1,45 @@
+#ifndef LOCALTIME64_H
+#    define LOCALTIME64_H
+
+/* Configuration. */
+/* Define as appropriate for your system */
+/*
+   HAS_TIMEGM
+   Defined if your system has timegm()
+
+   HAS_TM_TM_GMTOFF
+   Defined if your tm struct has a "tm_gmtoff" element.
+
+   HAS_TM_TM_ZONE
+   Defined if your tm struct has a "tm_zone" element.
+
+   SYSTEM_LOCALTIME_MAX
+   SYSTEM_LOCALTIME_MIN
+   SYSTEM_GMTIME_MAX
+   SYSTEM_GMTIME_MIN
+   Maximum and minimum values your system's gmtime() and localtime()
+   can handle.
+
+   USE_SYSTEM_LOCALTIME
+   USE_SYSTEM_GMTIME
+   Should we use the system functions if the time is inside their range?
+*/
+#define SYSTEM_LOCALTIME_MAX    LOCALTIME_MAX
+#define SYSTEM_LOCALTIME_MIN    LOCALTIME_MIN
+#define SYSTEM_GMTIME_MAX       GMTIME_MAX
+#define SYSTEM_GMTIME_MIN       GMTIME_MIN
+
+/* The system localtime will be faster and more correct inside its range */
+#define USE_SYSTEM_LOCALTIME    1
+#define USE_SYSTEM_GMTIME       1
+   
+
+/* 64 bit types.  Set as appropriate for your system. */
+typedef Quad_t               Time64_T;
+typedef Quad_t               Int64;
+
+struct tm *gmtime64_r    (const Time64_T *, struct tm *);
+struct tm *localtime64_r (const Time64_T *, struct tm *);
+Time64_T   timegm64      (struct tm *);
+
+#endif
diff --git a/pp_sys.c b/pp_sys.c
index 481864b..ad39804 100644
--- a/pp_sys.c
+++ b/pp_sys.c
@@ -27,6 +27,8 @@
 #include "EXTERN.h"
 #define PERL_IN_PP_SYS_C
 #include "perl.h"
+#include "localtime64.h"
+#include "localtime64.c"
 
 #ifdef I_SHADOW
 /* Shadow password support for solaris - pdo@cs.umd.edu
@@ -4446,60 +4448,66 @@ PP(pp_gmtime)
 {
     dVAR;
     dSP;
-    Time_t when;
-    const struct tm *tmbuf;
+    Time64_T when;
+    struct tm tmbuf;
+    struct tm *err;
     static const char * const dayname[] =
 	{"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
     static const char * const monname[] =
 	{"Jan", "Feb", "Mar", "Apr", "May", "Jun",
 	 "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
 
-    if (MAXARG < 1)
-	(void)time(&when);
+    if (MAXARG < 1) {
+	time_t now;
+	(void)time(&now);
+	when = (Time64_T)now;
+    }
     else
-#ifdef BIG_TIME
-	when = (Time_t)SvNVx(POPs);
-#else
-	when = (Time_t)SvIVx(POPs);
-#endif
+	when = (Time64_T)SvNVx(POPs);
 
     if (PL_op->op_type == OP_LOCALTIME)
-#ifdef LOCALTIME_EDGECASE_BROKEN
-	tmbuf = S_my_localtime(aTHX_ &when);
-#else
-	tmbuf = localtime(&when);
-#endif
+        err = localtime64_r(&when, &tmbuf);
     else
-	tmbuf = gmtime(&when);
+	err = gmtime64_r(&when, &tmbuf);
 
-    if (GIMME != G_ARRAY) {
+    if( err == NULL ) {
+	char *opname = PL_op->op_type == OP_LOCALTIME ? "localtime" : "gmtime";
+	Perl_warner(aTHX_ packWARN(WARN_OVERFLOW),
+		    "%s under/overflowed the year", opname);
+    }
+
+    if (GIMME != G_ARRAY) {	/* scalar context */
 	SV *tsv;
         EXTEND(SP, 1);
         EXTEND_MORTAL(1);
-	if (!tmbuf)
+	if (err == NULL)
 	    RETPUSHUNDEF;
+
 	tsv = Perl_newSVpvf(aTHX_ "%s %s %2d %02d:%02d:%02d %d",
-			    dayname[tmbuf->tm_wday],
-			    monname[tmbuf->tm_mon],
-			    tmbuf->tm_mday,
-			    tmbuf->tm_hour,
-			    tmbuf->tm_min,
-			    tmbuf->tm_sec,
-			    tmbuf->tm_year + 1900);
+			    dayname[tmbuf.tm_wday],
+			    monname[tmbuf.tm_mon],
+			    tmbuf.tm_mday,
+			    tmbuf.tm_hour,
+			    tmbuf.tm_min,
+			    tmbuf.tm_sec,
+			    tmbuf.tm_year + 1900);
 	mPUSHs(tsv);
     }
-    else if (tmbuf) {
+    else {			/* list context */
+	if ( err == NULL )
+	    RETURN;
+
         EXTEND(SP, 9);
         EXTEND_MORTAL(9);
-        mPUSHi(tmbuf->tm_sec);
-	mPUSHi(tmbuf->tm_min);
-	mPUSHi(tmbuf->tm_hour);
-	mPUSHi(tmbuf->tm_mday);
-	mPUSHi(tmbuf->tm_mon);
-	mPUSHi(tmbuf->tm_year);
-	mPUSHi(tmbuf->tm_wday);
-	mPUSHi(tmbuf->tm_yday);
-	mPUSHi(tmbuf->tm_isdst);
+        mPUSHi(tmbuf.tm_sec);
+	mPUSHi(tmbuf.tm_min);
+	mPUSHi(tmbuf.tm_hour);
+	mPUSHi(tmbuf.tm_mday);
+	mPUSHi(tmbuf.tm_mon);
+	mPUSHi(tmbuf.tm_year);
+	mPUSHi(tmbuf.tm_wday);
+	mPUSHi(tmbuf.tm_yday);
+	mPUSHi(tmbuf.tm_isdst);
     }
     RETURN;
 }
diff --git a/t/op/time.t b/t/op/time.t
index 8b2f07d..a67dead 100755
--- a/t/op/time.t
+++ b/t/op/time.t
@@ -1,14 +1,12 @@
 #!./perl
 
-$does_gmtime = gmtime(time);
-
 BEGIN {
     chdir 't' if -d 't';
     @INC = '../lib';
     require './test.pl';
 }
 
-plan tests => 8;
+plan tests => 32;
 
 ($beguser,$begsys) = times;
 
@@ -32,7 +30,9 @@ ok($i >= 2_000_000, 'very basic times test');
 ($xsec,$foo) = localtime($now);
 $localyday = $yday;
 
-ok($sec != $xsec && $mday && $year,             'localtime() list context');
+isnt($sec, $xsec),      'localtime() list context';
+ok $mday,               '  month day';
+ok $year,               '  year';
 
 ok(localtime() =~ /^(Sun|Mon|Tue|Wed|Thu|Fri|Sat)[ ]
                     (Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)[ ]
@@ -56,13 +56,13 @@ $ENV{TZ} = "GMT+5";
 ok($hour != $hour2,                             'changes to $ENV{TZ} respected');
 }
 
-SKIP: {
-    skip "No gmtime()", 3 unless $does_gmtime;
 
 ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = gmtime($beg);
 ($xsec,$foo) = localtime($now);
 
-ok($sec != $xsec && $mday && $year,             'gmtime() list context');
+isnt($sec, $xsec),      'gmtime() list conext';
+ok $mday,               '  month day';
+ok $year,               '  year';
 
 my $day_diff = $localyday - $yday;
 ok( grep({ $day_diff == $_ } (0, 1, -1, 364, 365, -364, -365)),
@@ -76,4 +76,49 @@ ok(gmtime() =~ /^(Sun|Mon|Tue|Wed|Thu|Fri|Sat)[ ]
                /x,
    'gmtime(), scalar context'
   );
+
+
+
+# Test gmtime over a range of times.
+{
+    # gm/localtime is limited by the size of tm_year which might be as small as 16 bits
+    my %tests = (
+        # time_t         gmtime list                          scalar
+        -2**35        => [52, 13, 20, 7, 2, -1019, 5, 65, 0, "Fri Mar  7 20:13:52 881"],
+        -2**32        => [44, 31, 17, 24, 10, -67, 0, 327, 0, "Sun Nov 24 17:31:44 1833"],
+        -2**31        => [52, 45, 20, 13, 11, 1, 5, 346, 0, "Fri Dec 13 20:45:52 1901"],
+        0             => [0, 0, 0, 1, 0, 70, 4, 0, 0, "Thu Jan  1 00:00:00 1970"],
+        2**30         => [4, 37, 13, 10, 0, 104, 6, 9, 0, "Sat Jan 10 13:37:04 2004"],
+        2**31         => [8, 14, 3, 19, 0, 138, 2, 18, 0, "Tue Jan 19 03:14:08 2038"],
+        2**32         => [16, 28, 6, 7, 1, 206, 0, 37, 0, "Sun Feb  7 06:28:16 2106"],
+        2**39         => [8, 18, 12, 25, 0, 17491, 2, 24, 0, "Tue Jan 25 12:18:08 19391"],
+    );
+
+    for my $time (keys %tests) {
+        my @expected  = @{$tests{$time}};
+        my $scalar    = pop @expected;
+
+        ok eq_array([gmtime($time)], \@expected),  "gmtime($time) list context";
+        is scalar gmtime($time), $scalar,       "  scalar";
+    }
+}
+
+
+# Test localtime
+{
+    # We pick times which fall in the middle of a month, so the month and year should be
+    # the same regardless of the time zone.
+    my %tests = (
+        # time_t           month, year,  scalar
+        5000000000      => [5,  228,     qr/Jun \d+ .* 2128$/],
+        1163500000      => [10, 106,     qr/Nov \d+ .* 2006$/],
+    );
+
+    for my $time (keys %tests) {
+        my @expected  = @{$tests{$time}};
+        my $scalar    = pop @expected;
+
+        ok eq_array([(localtime($time))[4,5]], \@expected),  "localtime($time) list context";
+        like scalar localtime($time), $scalar,       "  scalar";
+    }
 }

Follow-Ups from:
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