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/*
 *  R : A Computer Language for Statistical Data Analysis
 *  Copyright (C) 2000-2015  The R Core Team.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, a copy is available at
 *  http://www.r-project.org/Licenses/
 *
 *
 *      Interfaces to POSIX date-time conversion functions.
 */

/*
    These use POSIX functions which are now also part of C99 so are
    almost universally available, albeit with more room for
    implementation variations.

    A particular problem is the setting of the timezone TZ on
    Unix/Linux.  POSIX appears to require it, yet older Linux systems
    do not set it and do not give the correct results/crash strftime
    if it is not set (or even if it is: see the workaround below).  We
    use unsetenv() to work around this: that is a BSD (and POSIX 2001)
    construct but seems to be available on the affected platforms.
*/

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <Rmath.h> // Rexp10

// to get tm_zone, tm_gmtoff defined in glibc.
// some other header, e.g. math.h, might define the macro.
#if defined HAVE_FEATURES_H
# include <features.h>
# ifdef __GNUC_PREREQ
#  if __GNUC_PREREQ(2,20) && !defined(_DEFAULT_SOURCE_)
#   define _DEFAULT_SOURCE 1
#  endif
# endif
#endif
#if defined(HAVE_GLIBC2) && !defined(_DEFAULT_SOURCE_) && !defined(_BSD_SOURCE)
# define _BSD_SOURCE 1
#endif
#include <time.h>

#include <errno.h>

/* 

There are two implementation paths here.

1) Use the system functions for mktime, gmtime[_r], localtime[_r], strftime.
   Use the system time_t, struct tm and time-zone tables.

2) Use substitutes from src/extra/tzone for mktime, gmtime, localtime,
   strftime with a R_ prefix.  The system strftime is used for
   locale-dependent names in R_strptime and R_strftime.  This uses the
   time-zone tables shipped with R and installed into
   R_HOME/share/zoneinfo .

   Our own versions of time_t (64-bit) and struct tm (including the
   BSD-style fields tm_zone and tm_gmtoff) are used.

For path 1), the system facilities are used for 1902-2037 and outside
those limits where there is a 64-bit time_t and the conversions work
(most OSes currently have only 32-bit time-zone tables).  Otherwise
there is code below to extrapolate from 1902-2037.

Path 2) was added for R 3.1.0 and is the only one supported on
Windows: it is the default on OS X.  The only currently (Jan 2014)
known OS with 64-bit time_t and complete tables is Linux.

*/

#ifdef USE_INTERNAL_MKTIME
# include "datetime.h"
# undef HAVE_LOCAL_TIME_R
# define HAVE_LOCAL_TIME_R 1
# undef HAVE_TM_ZONE
# define HAVE_TM_ZONE 1
# undef HAVE_TM_GMTOFF
# define HAVE_TM_GMTOFF 1
# undef MKTIME_SETS_ERRNO
# define MKTIME_SETS_ERRNO
# undef HAVE_WORKING_64BIT_MKTIME
# define HAVE_WORKING_64BIT_MKTIME 1
#else

typedef struct tm stm;
#define R_tzname tzname
# if defined(__CYGWIN__)
extern __declspec(dllimport) char *tzname[2];
# else
extern char *tzname[2];
# endif

#endif

#include <stdlib.h> /* for setenv or putenv */
#include <Defn.h>
#include <Internal.h>

/* Substitute based on glibc code. */
#include "Rstrptime.h"

static const int days_in_month[12] =
{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

#define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0) || ((y) % 400) == 0)
#define days_in_year(year) (isleap(year) ? 366 : 365)

/*
  Adjust a struct tm to be a valid date-time.
  Return 0 if valid, -1 if invalid and uncorrectable, or a positive
  integer approximating the number of corrections needed.
  */
static int validate_tm (stm *tm)
{
    int tmp, res = 0;

    if (tm->tm_sec < 0 || tm->tm_sec > 60) { /* 61 POSIX, 60 draft ISO C */
    res++;
    tmp = tm->tm_sec/60;
    tm->tm_sec -= 60 * tmp; tm->tm_min += tmp;
    if(tm->tm_sec < 0) {tm->tm_sec += 60; tm->tm_min--;}
    }

    if (tm->tm_min < 0 || tm->tm_min > 59) {
    res++;
    tmp = tm->tm_min/60;
    tm->tm_min -= 60 * tmp; tm->tm_hour += tmp;
    if(tm->tm_min < 0) {tm->tm_min += 60; tm->tm_hour--;}
    }

    if(tm->tm_hour == 24 && tm->tm_min == 0 && tm->tm_sec == 0) {
    tm->tm_hour = 0; tm->tm_mday++;
    if(tm->tm_mon >= 0 && tm->tm_mon <= 11) {
        if(tm->tm_mday > days_in_month[tm->tm_mon] +
           ((tm->tm_mon==1 && isleap(1900+tm->tm_year) ? 1 : 0))) {
           tm->tm_mon++; tm->tm_mday = 1;
           if(tm->tm_mon == 12) {
               tm->tm_year++; tm->tm_mon = 0;
           }
           }
    }
    }
    if (tm->tm_hour < 0 || tm->tm_hour > 23) {
    res++;
    tmp = tm->tm_hour/24;
    tm->tm_hour -= 24 * tmp; tm->tm_mday += tmp;
    if(tm->tm_hour < 0) {tm->tm_hour += 24; tm->tm_mday--;}
    }

    /* defer fixing mday until we know the year */
    if (tm->tm_mon < 0 || tm->tm_mon > 11) {
    res++;
    tmp = tm->tm_mon/12;
    tm->tm_mon -= 12 * tmp; tm->tm_year += tmp;
    if(tm->tm_mon < 0) {tm->tm_mon += 12; tm->tm_year--;}
    }

    /* A limit on the loops of about 3000x round */
    if(tm->tm_mday < -1000000 || tm->tm_mday > 1000000) return -1;

    if(abs(tm->tm_mday) > 366) {
    res++;
    /* first spin back until January */
    while(tm->tm_mon > 0) {
        --tm->tm_mon;
        tm->tm_mday += days_in_month[tm->tm_mon] +
        ((tm->tm_mon==1 && isleap(1900+tm->tm_year))? 1 : 0);
    }
    /* then spin on/back by years */
    while(tm->tm_mday < 1) {
        --tm->tm_year;
        tm->tm_mday += 365 + (isleap(1900+tm->tm_year)? 1 : 0);
    }
    while(tm->tm_mday >
          (tmp = 365 + (isleap(1900+tm->tm_year)? 1 : 0))) {
        tm->tm_mday -= tmp; tm->tm_year++;
    }
    }

    while(tm->tm_mday < 1) {
    res++;
    if(--tm->tm_mon < 0) {tm->tm_mon += 12; tm->tm_year--;}
    tm->tm_mday += days_in_month[tm->tm_mon] +
        ((tm->tm_mon==1 && isleap(1900+tm->tm_year))? 1 : 0);
    }

    while(tm->tm_mday >
      (tmp = days_in_month[tm->tm_mon] +
       ((tm->tm_mon==1 && isleap(1900+tm->tm_year))? 1 : 0))) {
    res++;
    if(++tm->tm_mon > 11) {tm->tm_mon -= 12; tm->tm_year++;}
    tm->tm_mday -= tmp;
    }
    return res;
}


/* Substitute for mktime -- no checking, always in GMT */
static double mktime00 (stm *tm)
{
    int day = 0;
    int year, year0;
    double excess = 0.0;

    day = tm->tm_mday - 1;
    year0 = 1900 + tm->tm_year;
    /* safety check for unbounded loops */
    if (year0 > 3000) {
    excess = (int)(year0/2000) - 1;
    year0 -= (int)(excess * 2000);
    } else if (year0 < 0) {
    excess = -1 - (int)(-year0/2000);
    year0 -= (int)(excess * 2000);
    }

    for(int i = 0; i < tm->tm_mon; i++) day += days_in_month[i];
    if (tm->tm_mon > 1 && isleap(year0)) day++;
    tm->tm_yday = day;

    if (year0 > 1970) {
    for (year = 1970; year < year0; year++)
        day += days_in_year(year);
    } else if (year0 < 1970) {
    for (year = 1969; year >= year0; year--)
        day -= days_in_year(year);
    }

    /* weekday: Epoch day was a Thursday */
    if ((tm->tm_wday = (day + 4) % 7) < 0) tm->tm_wday += 7;

    return tm->tm_sec + (tm->tm_min * 60) + (tm->tm_hour * 3600)
    + (day + excess * 730485) * 86400.0;
}

#ifdef USE_INTERNAL_MKTIME
/* Interface to mktime or mktime00 */
static double mktime0 (stm *tm, const int local)
{
    if(validate_tm(tm) < 0) {
#ifdef EOVERFLOW
    errno = EOVERFLOW;
#else
    errno = 79;
#endif
    return -1.;
    }
    return local ? R_mktime(tm) : mktime00(tm);
}

/* Interface to localtime_r or gmtime_r */
static stm * localtime0(const double *tp, const int local, stm *ltm)
{
    time_t t = (time_t) *tp;
    return local ? R_localtime_r(&t, ltm) : R_gmtime_r(&t, ltm);
}

#else
/* The glibc in RH8.0 was broken and assumed that dates before
   1970-01-01 do not exist.  So does Windows, but its code was replaced
   in R 2.7.0.  As from 1.6.2, test the actual mktime code and cache
   the result on glibc >= 2.2. (It seems this started between 2.2.5
   and 2.3, and RH8.0 had an unreleased version in that gap.)

   Sometime in late 2004 this was reverted in glibc.
*/

static Rboolean have_broken_mktime(void)
{
#if defined(_AIX)
    return TRUE;  // maybe not so for AIX >= 6, which allegedly uses Olson code
#elif defined(__GLIBC__) && defined(__GLIBC_MINOR__) && __GLIBC__ == 2 && __GLIBC_MINOR__ >= 2 &&  __GLIBC_MINOR__ < 10
    static int test_result = -1;

    if (test_result == -1) {
    stm t;
    time_t res;
    t.tm_sec = t.tm_min = t.tm_hour = 0;
    t.tm_mday = t.tm_mon = 1;
    t.tm_year = 68;
    t.tm_isdst = -1;
    res = mktime(&t);
    test_result = (res == (time_t)-1);
    }
    return test_result > 0;
#else
    return FALSE;
#endif
}

#ifndef HAVE_POSIX_LEAPSECONDS
/* There have (2015/07) been 26 leapseconds: see .leap.seconds in R
 */
static int n_leapseconds = 26;
static const time_t leapseconds[] =
{  78796800, 94694400,126230400,157766400,189302400,220924800,252460800,
  283996800,315532800,362793600,394329600,425865600,489024000,567993600,
  631152000,662688000,709948800,741484800,773020800,820454400,867715200,
   915148800,1136073600,1230768000,1341100800,1435708800};
#endif

static double guess_offset (stm *tm)
{
    double offset, offset1, offset2;
    int i, wday, year, oldmonth, oldisdst, oldmday;
    stm oldtm;
    /*
       Adjust as best we can for timezones: if isdst is unknown, use
       the smaller offset at same day in Jan or July of a valid year.
       We don't know the timezone rules, but if we choose a year with
       July 1 on the same day of the week we will likely get guess
       right (since they are usually on Sunday mornings not in Jan/Feb).

       Update for 2.7.0: no one had DST before 1916, so just use the offset
       in 1902, if available.
    */

    memcpy(&oldtm, tm, sizeof(stm));
    if(!have_broken_mktime() && tm->tm_year < 2) { /* no DST */
    tm->tm_year = 2;
    mktime(tm);
    offset1 = (double) mktime(tm) - mktime00(tm);
    memcpy(tm, &oldtm, sizeof(stm));
    tm->tm_isdst = 0;
    return offset1;
    }
    oldmonth = tm->tm_mon;
    oldmday = tm->tm_mday;
    /* We know there was no DST prior to 1916 */
    oldisdst = (tm->tm_year < 16) ? 0 : tm->tm_isdst;

    /* so now look for a suitable year */
    tm->tm_mon = 6;
    tm->tm_mday = 1;
    tm->tm_isdst = -1;
    mktime00(tm);  /* to get wday valid */
    wday = tm->tm_wday;
    if (oldtm.tm_year > 137) { /* in the unknown future */
    for(i = 130; i < 137; i++) { /* These cover all the possibilities */
        tm->tm_year = i;
        mktime(tm);
        if(tm->tm_wday == wday) break;
    }
    } else { /* a benighted OS with date before 1970 */
    /* We could not use 1970 because of the Windows bug with
       1970-01-01 east of GMT. */
    for(i = 71; i < 82; i++) { /* These cover all the possibilities */
        tm->tm_year = i;
        mktime(tm);
        if(tm->tm_wday == wday) break;
    }
    }
    year = i;

    /* Now look up offset in January */
    tm->tm_mday = oldmday;
    tm->tm_mon = 0;
    tm->tm_year = year;
    tm->tm_isdst = -1;
    offset1 = (double) mktime(tm) - mktime00(tm);
    /* and in July */
    tm->tm_year = year;
    tm->tm_mon = 6;
    tm->tm_isdst = -1;
    offset2 = (double) mktime(tm) - mktime00(tm);
    if(oldisdst > 0) {
    offset = (offset1 > offset2) ? offset2 : offset1;
    } else {
    offset = (offset1 > offset2) ? offset1 : offset2;
    }
    /* now try to guess dst if unknown */
    tm->tm_mon = oldmonth;
    tm->tm_isdst = -1;
    if(oldisdst < 0) {
    offset1 = (double) mktime(tm) - mktime00(tm);
    oldisdst = (offset1 < offset) ? 1:0;
    if(oldisdst) offset = offset1;
    }
    /* restore all as mktime might alter it */
    memcpy(tm, &oldtm, sizeof(stm));
    /* and then set isdst */
    tm->tm_isdst = oldisdst;
    return offset;
}

/* Interface to mktime or mktime00 */
static double mktime0 (stm *tm, const int local)
{
    double res;
    Rboolean OK;

    if(validate_tm(tm) < 0) {
#ifdef EOVERFLOW
    errno = EOVERFLOW;
#else
    errno = 79;
#endif
    return -1.;
    }
    if(!local) return mktime00(tm);

/* OS X 10.9 gives -1 for dates prior to 1902, and ignores DST after 2037 */
#ifdef HAVE_WORKING_64BIT_MKTIME
    if(sizeof(time_t) == 8)
    OK = !have_broken_mktime() || tm->tm_year >= 70;
    else
#endif
    OK = tm->tm_year < 138 && tm->tm_year >= (have_broken_mktime() ? 70 : 02);
    if(OK) {
    res = (double) mktime(tm);
    if (res == -1.) return res;
#ifndef HAVE_POSIX_LEAPSECONDS
    for(int i = 0; i < n_leapseconds; i++)
        if(res > leapseconds[i]) res -= 1.0;
#endif
    return res;
/* watch the side effect here: both calls alter their arg */
    } else return guess_offset(tm) + mktime00(tm);
}

/* Interface for localtime or gmtime or internal substitute */
static stm * localtime0(const double *tp, const int local, stm *ltm)
{
    double d = *tp;
    int y, tmp;
    time_t t;

    Rboolean OK;
/* as mktime is broken, do not trust localtime */
#ifdef HAVE_WORKING_64BIT_MKTIME
    if (sizeof(time_t) == 8)
    OK = !have_broken_mktime() || d > 0.;
    else
#endif
    OK = d < 2147483647.0 && 
        d > (have_broken_mktime() ? 0. : -2147483647.0);
    if(OK) {
    t = (time_t) d;
    /* if d is negative and non-integer then t will be off by one day
       since we really need floor(). But floor() is slow, so we just
       fix t instead as needed. */
    if (d < 0.0 && (double) t != d) t--;
#ifndef HAVE_POSIX_LEAPSECONDS
    for(int y = 0; y < n_leapseconds; y++) if(t > leapseconds[y] + y - 1) t++;
#endif
#ifdef HAVE_LOCALTIME_R
    return local ? localtime_r(&t, ltm) : gmtime_r(&t, ltm);
#else
    return local ? localtime(&t) : gmtime(&t);
#endif
    }
    
    /* internal substitute code.
       Like localtime, this returns a pointer to a static struct tm */

    int day = (int) floor(d/86400.0);
    int left = (int) (d - day * 86400.0 + 1e-6); // allow for fractional secs

    static stm ltm0, *res = &ltm0;
    memset(res, 0, sizeof(stm));
    /* hour, min, and sec */
    res->tm_hour = left / 3600;
    left %= 3600;
    res->tm_min = left / 60;
    res->tm_sec = left % 60;

    /* weekday: 1970-01-01 was a Thursday */
    if ((res->tm_wday = ((4 + day) % 7)) < 0) res->tm_wday += 7;

    /* year & day within year */
    y = 1970;
    if (day >= 0)
    for ( ; day >= (tmp = days_in_year(y)); day -= tmp, y++);
    else
    for ( ; day < 0; --y, day += days_in_year(y) );

    y = res->tm_year = y - 1900;
    res->tm_yday = day;

    /* month within year */
    int mon;
    for (mon = 0;
     day >= (tmp = (days_in_month[mon]) + ((mon==1 && isleap(y+1900))?1:0));
     day -= tmp, mon++);
    res->tm_mon = mon;
    res->tm_mday = day + 1;

    if(local) {
    double shift;
    /*  daylight saving time is unknown */
    res->tm_isdst = -1;

    /* Try to fix up time zone differences: cf PR#15480 */
    int sdiff = (int)guess_offset(res);
    int diff = sdiff/60;
    // just in case secs are out of range and might affect this.
    shift = 60.*res->tm_hour + res->tm_min + res->tm_sec/60.;
    res->tm_min -= diff;
    res->tm_sec -= (sdiff % 60);
    validate_tm(res);
    res->tm_isdst = -1;
    /* now this might be a different day */
    if(shift - diff < 0.) {
        res->tm_yday--;
        res->tm_wday--;
    }
    else if(shift - diff >= 24. * 60.) {
        res->tm_yday++;
        res->tm_wday++;
    }
    int sdiff2 = (int)guess_offset(res);
    int diff2 = sdiff2/60;
    if(diff2 != diff) {
        res->tm_min += (diff - diff2);
        res->tm_sec += (sdiff % 60) - (sdiff2 % 60);
        validate_tm(res);
    }
#ifdef HAVE_TM_GMTOFF
    res->tm_gmtoff = -sdiff2;
#endif
    // No DST before 1916
    if(res->tm_year < 16) res->tm_isdst = 0;
    return res;
    } else {
    res->tm_isdst = 0; /* no dst in GMT */
    return res;
    }
}
#endif

static int set_tz(const char *tz, char *oldtz)
{
    char *p = NULL;
    int settz = 0;

    strcpy(oldtz, "");
    p = getenv("TZ");
    if(p) {
    if (strlen(p) > 1000)
        error("time zone specification is too long");
    strcpy(oldtz, p);
    }
#ifdef HAVE_SETENV
    if(setenv("TZ", tz, 1)) warning(_("problem with setting timezone"));
    settz = 1;
#elif defined(HAVE_PUTENV)
    {
    static char buff[1010];
    if (strlen(tz) > 1000)
        error("time zone specification is too long");
    strcpy(buff, "TZ="); strcat(buff, tz);
    if(putenv(buff)) warning(_("problem with setting timezone"));
    }
    settz = 1;
#else
    warning(_("cannot set timezones on this system"));
#endif
    tzset();
    return settz;
}

static void reset_tz(char *tz)
{
    if(strlen(tz)) {
#ifdef HAVE_SETENV
    if(setenv("TZ", tz, 1)) warning(_("problem with setting timezone"));
#elif defined(HAVE_PUTENV)
    {
        static char buff[200];
        strcpy(buff, "TZ="); strcat(buff, tz);
        if(putenv(buff)) warning(_("problem with setting timezone"));
    }
#endif
    } else {
#ifdef HAVE_UNSETENV
    unsetenv("TZ"); /* FreeBSD variants do not return a value */
#elif defined(HAVE_PUTENV_UNSET)
    if(putenv("TZ")) warning(_("problem with unsetting timezone"));
#elif defined(HAVE_PUTENV_UNSET2)
    if(putenv("TZ=")) warning(_("problem with unsetting timezone"));
#endif
    }
    tzset();
}

static void glibc_fix(stm *tm, int *invalid)
{
    /* set mon and mday which glibc does not always set.
       Use current year/... if none has been specified.

       Specifying mon but not mday nor yday is invalid.
    */
    time_t t = time(NULL);
    stm *tm0;
    int tmp;
#ifndef HAVE_POSIX_LEAPSECONDS
    t -= n_leapseconds;
#endif
#ifdef HAVE_LOCALTIME_R
    stm tm2;
    tm0 = localtime_r(&t, &tm2);
#else
    tm0 = localtime(&t);
#endif
    if(tm->tm_year == NA_INTEGER) tm->tm_year = tm0->tm_year;
    if(tm->tm_mon != NA_INTEGER && tm->tm_mday != NA_INTEGER) return;
    /* at least one of the month and the day of the month is missing */
    if(tm->tm_yday != NA_INTEGER) {
    /* since we have yday, let that take precedence over mon/mday */
    int yday = tm->tm_yday, mon = 0;
    while(yday >= (tmp = days_in_month[mon] +
              ((mon==1 && isleap(1900+tm->tm_year))? 1 : 0))) {
        yday -= tmp;
        mon++;
    }
    tm->tm_mon = mon;
    tm->tm_mday = yday + 1;
    } else {
    if(tm->tm_mday == NA_INTEGER) {
        if(tm->tm_mon != NA_INTEGER) {
        *invalid = 1;
        return;
        } else tm->tm_mday = tm0->tm_mday;
    }
    if(tm->tm_mon == NA_INTEGER) tm->tm_mon = tm0->tm_mon;
    }
}


static const char ltnames [][7] =
{ "sec", "min", "hour", "mday", "mon", "year", "wday", "yday", "isdst", 
  "zone",  "gmtoff"};


static void 
makelt(stm *tm, SEXP ans, R_xlen_t i, int valid, double frac_secs)
{
    if(valid) {
    REAL(VECTOR_ELT(ans, 0))[i] = tm->tm_sec + frac_secs;
    INTEGER(VECTOR_ELT(ans, 1))[i] = tm->tm_min;
    INTEGER(VECTOR_ELT(ans, 2))[i] = tm->tm_hour;
    INTEGER(VECTOR_ELT(ans, 3))[i] = tm->tm_mday;
    INTEGER(VECTOR_ELT(ans, 4))[i] = tm->tm_mon;
    INTEGER(VECTOR_ELT(ans, 5))[i] = tm->tm_year;
    INTEGER(VECTOR_ELT(ans, 6))[i] = tm->tm_wday;
    INTEGER(VECTOR_ELT(ans, 7))[i] = tm->tm_yday;
    INTEGER(VECTOR_ELT(ans, 8))[i] = tm->tm_isdst;
    } else {
    REAL(VECTOR_ELT(ans, 0))[i] = NA_REAL;
    for(int j = 1; j < 8; j++)
        INTEGER(VECTOR_ELT(ans, j))[i] = NA_INTEGER;
    INTEGER(VECTOR_ELT(ans, 8))[i] = -1;
    }
}


             /* --------- R interfaces --------- */

// We assume time zone names/abbreviations are ASCII, as all known ones are.

SEXP attribute_hidden do_asPOSIXlt(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP stz, x, ans, ansnames, klass, tzone;
    int isgmt = 0, valid, settz = 0;
    char oldtz[1001] = "";
    const char *tz = NULL;

    checkArity(op, args);
    PROTECT(x = coerceVector(CAR(args), REALSXP));
    if(!isString((stz = CADR(args))) || LENGTH(stz) != 1)
    error(_("invalid '%s' value"), "tz");
    tz = CHAR(STRING_ELT(stz, 0));
    if(strlen(tz) == 0) {
    /* do a direct look up here as this does not otherwise
       work on Windows */
    char *p = getenv("TZ");
    if(p) {
        stz = mkString(p); /* make a copy */
        tz = CHAR(STRING_ELT(stz, 0));
    }
    }
    PROTECT(stz); /* it might be new */
    if(strcmp(tz, "GMT") == 0  || strcmp(tz, "UTC") == 0) isgmt = 1;
    if(!isgmt && strlen(tz) > 0) settz = set_tz(tz, oldtz);
#ifdef USE_INTERNAL_MKTIME
    else R_tzsetwall(); // to get the system timezone recorded
#else
    tzset();
#endif

    // localtime may change tzname.
    if (isgmt) {
    PROTECT(tzone = mkString(tz));
    } else {
    PROTECT(tzone = allocVector(STRSXP, 3));
    SET_STRING_ELT(tzone, 0, mkChar(tz));
    SET_STRING_ELT(tzone, 1, mkChar(R_tzname[0]));
    SET_STRING_ELT(tzone, 2, mkChar(R_tzname[1]));
    }

    R_xlen_t n = XLENGTH(x);
#ifdef HAVE_TM_GMTOFF
    int nans = 11 - 2 * isgmt;
#else
    int nans = 10 - isgmt;
#endif
    PROTECT(ans = allocVector(VECSXP, nans));
    for(int i = 0; i < 9; i++)
    SET_VECTOR_ELT(ans, i, allocVector(i > 0 ? INTSXP : REALSXP, n));
    if(!isgmt) {
    SET_VECTOR_ELT(ans, 9, allocVector(STRSXP, n));
#ifdef HAVE_TM_GMTOFF
    SET_VECTOR_ELT(ans, 10, allocVector(INTSXP, n));
#endif
    }

    PROTECT(ansnames = allocVector(STRSXP, nans));
    for(int i = 0; i < nans; i++)
    SET_STRING_ELT(ansnames, i, mkChar(ltnames[i]));

    for(R_xlen_t i = 0; i < n; i++) {
    stm dummy, *ptm = &dummy;
    double d = REAL(x)[i];
    if(R_FINITE(d)) {
        ptm = localtime0(&d, 1 - isgmt, &dummy);
        /* in theory localtime/gmtime always return a valid
           struct tm pointer, but Windows uses NULL for error
           conditions (like negative times). */
        valid = (ptm != NULL);
    } else valid = 0;
    makelt(ptm, ans, i, valid, d - floor(d));
    if(!isgmt) {
        char *p = "";
        // or ptm->tm_zone
        if(valid && ptm->tm_isdst >= 0) 
        p = R_tzname[ptm->tm_isdst];
        SET_STRING_ELT(VECTOR_ELT(ans, 9), i, mkChar(p));
#ifdef HAVE_TM_GMTOFF
        INTEGER(VECTOR_ELT(ans, 10))[i] = 
        valid ? (int)ptm->tm_gmtoff : NA_INTEGER;
#endif
    }
    }
    setAttrib(ans, R_NamesSymbol, ansnames);
    PROTECT(klass = allocVector(STRSXP, 2));
    SET_STRING_ELT(klass, 0, mkChar("POSIXlt"));
    SET_STRING_ELT(klass, 1, mkChar("POSIXt"));
    classgets(ans, klass);
    setAttrib(ans, install("tzone"), tzone);
    SEXP nm = getAttrib(x, R_NamesSymbol);
    if(! IS_R_NilValue(nm)) setAttrib(VECTOR_ELT(ans, 5), R_NamesSymbol, nm);
    UNPROTECT(6);

    if(settz) reset_tz(oldtz);
    return ans;
}

SEXP attribute_hidden do_asPOSIXct(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP stz, x, ans;
    R_xlen_t n = 0, nlen[9];
    int isgmt = 0, settz = 0;
    char oldtz[1001] = "";
    const char *tz = NULL;
    stm tm;
    double tmp;

    checkArity(op, args);
    PROTECT(x = duplicate(CAR(args))); /* coerced below */
    if(!isVectorList(x) || LENGTH(x) < 9)
    error(_("invalid '%s' argument"), "x");
    if(!isString((stz = CADR(args))) || LENGTH(stz) != 1)
    error(_("invalid '%s' value"), "tz");

    tz = CHAR(STRING_ELT(stz, 0));
    if(strlen(tz) == 0) {
    /* do a direct look up here as this does not otherwise
       work on Windows */
    char *p = getenv("TZ");
    if(p) {
        stz = mkString(p);
        tz = CHAR(STRING_ELT(stz, 0));
    }
    }
    PROTECT(stz); /* it might be new */
    if(strcmp(tz, "GMT") == 0  || strcmp(tz, "UTC") == 0) isgmt = 1;
    if(!isgmt && strlen(tz) > 0) settz = set_tz(tz, oldtz);
#ifdef USE_INTERNAL_MKTIME
    else R_tzsetwall(); // to get the system timezone recorded
#else
    tzset();
#endif

    for(int i = 0; i < 6; i++)
    if((nlen[i] = XLENGTH(VECTOR_ELT(x, i))) > n) n = nlen[i];
    if((nlen[8] = XLENGTH(VECTOR_ELT(x, 8))) > n) n = nlen[8];
    if(n > 0) {
    for(int i = 0; i < 6; i++)
        if(nlen[i] == 0)
        error(_("zero-length component in non-empty \"POSIXlt\" structure"));
    if(nlen[8] == 0)
        error(_("zero-length component in non-empty \"POSIXlt\" structure"));
    }
    /* coerce fields to integer or real */
    SET_VECTOR_ELT(x, 0, coerceVector(VECTOR_ELT(x, 0), REALSXP));
    for(int i = 0; i < 6; i++)
    SET_VECTOR_ELT(x, i, coerceVector(VECTOR_ELT(x, i),
                      i > 0 ? INTSXP: REALSXP));
    SET_VECTOR_ELT(x, 8, coerceVector(VECTOR_ELT(x, 8), INTSXP));

    PROTECT(ans = allocVector(REALSXP, n));
    for(R_xlen_t i = 0; i < n; i++) {
    double secs = REAL(VECTOR_ELT(x, 0))[i%nlen[0]], fsecs = floor(secs);
    // avoid (int) NAN
    tm.tm_sec   = R_FINITE(secs) ? (int) fsecs: NA_INTEGER;
    tm.tm_min   = INTEGER(VECTOR_ELT(x, 1))[i%nlen[1]];
    tm.tm_hour  = INTEGER(VECTOR_ELT(x, 2))[i%nlen[2]];
    tm.tm_mday  = INTEGER(VECTOR_ELT(x, 3))[i%nlen[3]];
    tm.tm_mon   = INTEGER(VECTOR_ELT(x, 4))[i%nlen[4]];
    tm.tm_year  = INTEGER(VECTOR_ELT(x, 5))[i%nlen[5]];
    /* mktime ignores tm.tm_wday and tm.tm_yday */
    tm.tm_isdst = isgmt ? 0:INTEGER(VECTOR_ELT(x, 8))[i%nlen[8]];
    if(!R_FINITE(secs) || tm.tm_min == NA_INTEGER ||
       tm.tm_hour == NA_INTEGER || tm.tm_mday == NA_INTEGER ||
       tm.tm_mon == NA_INTEGER || tm.tm_year == NA_INTEGER)
        REAL(ans)[i] = NA_REAL;
    else {
        errno = 0;
        tmp = mktime0(&tm, 1 - isgmt);
#ifdef MKTIME_SETS_ERRNO
        REAL(ans)[i] = errno ? NA_REAL : tmp + (secs - fsecs);
#else
        REAL(ans)[i] = ((tmp == -1.)
                /* avoid silly gotcha at epoch minus one sec */
                && (tm.tm_sec != 59)
                && ((tm.tm_sec = 58), (mktime0(&tm, 1 - isgmt) != -2.))
                ) ?
          NA_REAL : tmp + (secs - fsecs);
#endif
    }
    }

    if(settz) reset_tz(oldtz);

    UNPROTECT(3);
    return ans;
}

SEXP attribute_hidden do_formatPOSIXlt(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP x, sformat, ans, tz;
    R_xlen_t n = 0, m, N, nlen[9];
    int UseTZ, settz = 0;
    char buff[300];
    char oldtz[1001] = "";
    stm tm;

    checkArity(op, args);
    PROTECT(x = duplicate(CAR(args))); /* coerced below */
    if(!isVectorList(x) || LENGTH(x) < 9)
    error(_("invalid '%s' argument"), "x");
    if(!isString((sformat = CADR(args))) || XLENGTH(sformat) == 0)
    error(_("invalid '%s' argument"), "format");
    m = XLENGTH(sformat);
    UseTZ = asLogical(CADDR(args));
    if(UseTZ == NA_LOGICAL)
    error(_("invalid '%s' argument"), "usetz");
    tz = getAttrib(x, install("tzone"));

    const char *tz1;
    if (!isNull(tz) && strlen(tz1 = CHAR(STRING_ELT(tz, 0)))) {
    /* If the format includes %Z or %z
       we need to try to set TZ accordingly */
    int needTZ = 0;
    for(R_xlen_t i = 0; i < m; i++) {
        const char *p = translateChar(STRING_ELT(sformat, i));
        if (strstr(p, "%Z") || strstr(p, "%z")) {needTZ = 1; break;}
    }
    if(needTZ) settz = set_tz(tz1, oldtz);
    }

    /* workaround for glibc/FreeBSD/MacOS X strftime: they have
       non-POSIX/C99 time zone components
     */
    memset(&tm, 0, sizeof(tm));

    /* coerce fields to integer or real, find length of longest one */
    for(int i = 0; i < 9; i++) {
    nlen[i] = XLENGTH(VECTOR_ELT(x, i));
    if(nlen[i] > n) n = nlen[i];
    SET_VECTOR_ELT(x, i, coerceVector(VECTOR_ELT(x, i),
                      i > 0 ? INTSXP : REALSXP));
    }
    if(n > 0) {
    for(int i = 0; i < 9; i++)
        if(nlen[i] == 0)
        error(_("zero-length component in non-empty \"POSIXlt\" structure"));
    }
    if(n > 0) N = (m > n) ? m:n; else N = 0;
    PROTECT(ans = allocVector(STRSXP, N));
    char tm_zone[20];
    Rboolean have_zone = LENGTH(x) >= 10 && LENGTH(VECTOR_ELT(x, 9)) == n;
    for(R_xlen_t i = 0; i < N; i++) {
    double secs = REAL(VECTOR_ELT(x, 0))[i%nlen[0]], fsecs = floor(secs);
    // avoid (int) NAN
    tm.tm_sec   = R_FINITE(secs) ? (int) fsecs: NA_INTEGER;
    tm.tm_min   = INTEGER(VECTOR_ELT(x, 1))[i%nlen[1]];
    tm.tm_hour  = INTEGER(VECTOR_ELT(x, 2))[i%nlen[2]];
    tm.tm_mday  = INTEGER(VECTOR_ELT(x, 3))[i%nlen[3]];
    tm.tm_mon   = INTEGER(VECTOR_ELT(x, 4))[i%nlen[4]];
    tm.tm_year  = INTEGER(VECTOR_ELT(x, 5))[i%nlen[5]];
    tm.tm_wday  = INTEGER(VECTOR_ELT(x, 6))[i%nlen[6]];
    tm.tm_yday  = INTEGER(VECTOR_ELT(x, 7))[i%nlen[7]];
    tm.tm_isdst = INTEGER(VECTOR_ELT(x, 8))[i%nlen[8]];
    if(have_zone) {
        strncpy(tm_zone, CHAR(STRING_ELT(VECTOR_ELT(x, 9), i)), 20);
            tm_zone[20 - 1] = '\0';
#ifdef HAVE_TM_ZONE
        tm.tm_zone = tm_zone;
#elif defined USE_INTERNAL_MKTIME
        if(tm.tm_isdst >= 0) R_tzname[tm.tm_isdst] = tm_zone;
#else
        // The system one, as we use system strftime here
        if(tm.tm_isdst >= 0) tzname[tm.tm_isdst] = tm_zone;
#endif
#ifdef HAVE_TM_GMTOFF
        int tmp = INTEGER(VECTOR_ELT(x, 10))[i%n];
        tm.tm_gmtoff = (tmp == NA_INTEGER) ? 0 : tmp;
#endif
    }
    if(!R_FINITE(secs) || tm.tm_min == NA_INTEGER ||
       tm.tm_hour == NA_INTEGER || tm.tm_mday == NA_INTEGER ||
       tm.tm_mon == NA_INTEGER || tm.tm_year == NA_INTEGER) {
        SET_STRING_ELT(ans, i, NA_STRING);
    } else {
        if(validate_tm(&tm) < 0) SET_STRING_ELT(ans, i, NA_STRING);
        else {
        const char *q = translateChar(STRING_ELT(sformat, i%m));
        int n = (int) strlen(q) + 50;
        char buf2[n];
        const char *p;
#ifdef OLD_Win32
        /* We want to override Windows' TZ names */
        p = strstr(q, "%Z");
        if (p) {
            memset(buf2, 0, n);
            strncpy(buf2, q, p - q);
            if(have_zone) 
            strcat(buf2, tm_zone);
            else
            strcat(buf2, tm.tm_isdst > 0 ? R_tzname[1] : R_tzname[0]);
            strcat(buf2, p+2);
        } else
#endif
            strcpy(buf2, q);

        p = strstr(q, "%OS");
        if(p) {
            /* FIXME some of this should be outside the loop */
            int ns, nused = 4;
            char *p2 = strstr(buf2, "%OS");
            *p2 = '\0';
            ns = *(p+3) - '0';
            if(ns < 0 || ns > 9) { /* not a digit */
            ns = asInteger(GetOption1(install("digits.secs")));
            if(ns == NA_INTEGER) ns = 0;
            nused = 3;
            }
            if(ns > 6) ns = 6;
            if(ns > 0) {
            /* truncate to avoid nuisances such as PR#14579 */
            double s = secs, t = Rexp10((double) ns);
            s = ((int) (s*t))/t;
            sprintf(p2, "%0*.*f", ns+3, ns, s);
            strcat(buf2, p+nused);
            } else {
            strcat(p2, "%S");
            strcat(buf2, p+nused);
            }
        }
        // The overflow behaviour is not determined by C99.
        // We assume truncation, and ensure termination.
#ifdef USE_INTERNAL_MKTIME
        R_strftime(buff, 256, buf2, &tm);
#else
        strftime(buff, 256, buf2, &tm);
#endif
        buff[256] = '\0';
        // Now assume tzone abbreviated name is < 40 bytes,
        // but they are currently 3 or 4 bytes.
        if(UseTZ) {
            if(LENGTH(x) >= 10) {
            const char *p = CHAR(STRING_ELT(VECTOR_ELT(x, 9), i));
            if(strlen(p)) {strcat(buff, " "); strcat(buff, p);}
            } else if(!isNull(tz)) {
            int ii = 0;
            if(LENGTH(tz) == 3) {
                if(tm.tm_isdst > 0) ii = 2;
                else if(tm.tm_isdst == 0) ii = 1;
                else ii = 0; /* Use base timezone name */
            }
            const char *p = CHAR(STRING_ELT(tz, ii));
            if(strlen(p)) {strcat(buff, " "); strcat(buff, p);}
            }
        }
        SET_STRING_ELT(ans, i, mkChar(buff));
        }
    }
    }
    if(settz) reset_tz(oldtz);
    UNPROTECT(2);
    return ans;
}


SEXP attribute_hidden do_strptime(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP x, sformat, ans, ansnames, klass, stz, tzone = R_NilValue;
    int invalid, isgmt = 0, settz = 0, offset;
    stm tm, tm2, *ptm = &tm;
    const char *tz = NULL;
    char oldtz[1001] = "";
    double psecs = 0.0;
    R_xlen_t n, m, N;

    checkArity(op, args);
    if(!isString((x = CAR(args))))
    error(_("invalid '%s' argument"), "x");
    if(!isString((sformat = CADR(args))) || XLENGTH(sformat) == 0)
    error(_("invalid '%s' argument"), "x");
    if(!isString((stz = CADDR(args))) || LENGTH(stz) != 1)
    error(_("invalid '%s' value"), "tz");
    tz = CHAR(STRING_ELT(stz, 0));
    if(strlen(tz) == 0) {
    /* do a direct look up here as this does not otherwise
       work on Windows */
    char *p = getenv("TZ");
    if(p) {
        stz = mkString(p);
        tz = CHAR(STRING_ELT(stz, 0));
    }
    }
    PROTECT(stz); /* it might be new */
    if(strcmp(tz, "GMT") == 0  || strcmp(tz, "UTC") == 0) isgmt = 1;
    if(!isgmt && strlen(tz) > 0) settz = set_tz(tz, oldtz);
#ifdef USE_INTERNAL_MKTIME
    else R_tzsetwall(); // to get the system timezone recorded
#else
    tzset();
#endif

    // in case this gets changed by conversions.
    if (isgmt) {
    PROTECT(tzone = mkString(tz));
    } else if(strlen(tz)) {
    PROTECT(tzone = allocVector(STRSXP, 3));
    SET_STRING_ELT(tzone, 0, mkChar(tz));
    SET_STRING_ELT(tzone, 1, mkChar(R_tzname[0]));
    SET_STRING_ELT(tzone, 2, mkChar(R_tzname[1]));
    
    } else PROTECT(tzone); // for balance

    n = XLENGTH(x); m = XLENGTH(sformat);
    if(n > 0) N = (m > n) ? m : n; else N = 0;

#ifdef HAVE_TM_GMTOFF
    int nans = 11 - 2 * isgmt;
#else
    int nans = 10 - isgmt;
#endif
    PROTECT(ans = allocVector(VECSXP, nans));
    for(int i = 0; i < 9; i++)
    SET_VECTOR_ELT(ans, i, allocVector(i > 0 ? INTSXP : REALSXP, N));
    if(!isgmt) {
    SET_VECTOR_ELT(ans, 9, allocVector(STRSXP, n));
#ifdef HAVE_TM_GMTOFF
    SET_VECTOR_ELT(ans, 10, allocVector(INTSXP, n));
#endif
    }

    PROTECT(ansnames = allocVector(STRSXP, nans));
    for(int i = 0; i < nans; i++)
    SET_STRING_ELT(ansnames, i, mkChar(ltnames[i]));


    for(R_xlen_t i = 0; i < N; i++) {
    /* for glibc's sake. That only sets some unspecified fields,
       sometimes. */
    memset(&tm, 0, sizeof(stm));
    tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
    tm.tm_year = tm.tm_mon = tm.tm_mday = tm.tm_yday =
        tm.tm_wday = NA_INTEGER;
#ifdef HAVE_TM_GMTOFF
    tm.tm_gmtoff = (long) NA_INTEGER;
    tm.tm_isdst = -1;
#endif
    offset = NA_INTEGER;
    invalid = IS_NA_STRING(STRING_ELT(x, i%n)) ||
        !R_strptime(translateChar(STRING_ELT(x, i%n)),
            translateChar(STRING_ELT(sformat, i%m)),
            &tm, &psecs, &offset);
    if(!invalid) {
        /* Solaris sets missing fields to 0 */
        if(tm.tm_mday == 0) tm.tm_mday = NA_INTEGER;
        if(tm.tm_mon == NA_INTEGER || tm.tm_mday == NA_INTEGER
           || tm.tm_year == NA_INTEGER)
        glibc_fix(&tm, &invalid);
        tm.tm_isdst = -1;
        if (offset != NA_INTEGER) {
#ifdef HAVE_TM_GMTOFF
        tm.tm_gmtoff = offset;
#endif
        /* we know the offset, but not the timezone
           so all we can do is to convert to time_t,
           adjust and convert back */
        double t0;
        memcpy(&tm2, &tm, sizeof(stm));
        t0 = mktime0(&tm2, 0);
        if (t0 != -1) {
            t0 -= offset; /* offset = -0800 is Seattle */
            ptm = localtime0(&t0, 1-isgmt, &tm2);
        } else invalid = 1;
        } else {
        /* we do want to set wday, yday, isdst, but not to
           adjust structure at DST boundaries */
        memcpy(&tm2, &tm, sizeof(stm));
        mktime0(&tm2, 1-isgmt); /* set wday, yday, isdst */
        tm.tm_wday = tm2.tm_wday;
        tm.tm_yday = tm2.tm_yday;
        tm.tm_isdst = isgmt ? 0: tm2.tm_isdst;
        }
        invalid = validate_tm(&tm) != 0;
    }
    makelt(ptm, ans, i, !invalid, psecs - floor(psecs));
    if(!isgmt) {
        const char *p = "";
        if(!invalid && tm.tm_isdst >= 0) {
#ifdef HAVE_TM_ZONE
        p = tm.tm_zone;
        if(!p)
#endif
            p = R_tzname[tm.tm_isdst];
        }
        SET_STRING_ELT(VECTOR_ELT(ans, 9), i, mkChar(p));
#ifdef HAVE_TM_GMTOFF
        INTEGER(VECTOR_ELT(ans, 10))[i] = 
        invalid ? NA_INTEGER : (int)tm.tm_gmtoff;
#endif
    }
    }

    setAttrib(ans, R_NamesSymbol, ansnames);
    PROTECT(klass = allocVector(STRSXP, 2));
    SET_STRING_ELT(klass, 0, mkChar("POSIXlt"));
    SET_STRING_ELT(klass, 1, mkChar("POSIXt"));
    classgets(ans, klass);
    if(settz) reset_tz(oldtz);
    if(isString(tzone)) setAttrib(ans, install("tzone"), tzone);

    UNPROTECT(5);
    return ans;
}

SEXP attribute_hidden do_D2POSIXlt(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP x, ans, ansnames, klass;
    R_xlen_t n;
    int valid, day, y, tmp, mon;
    stm tm;

    checkArity(op, args);
    PROTECT(x = coerceVector(CAR(args), REALSXP));
    n = XLENGTH(x);
    PROTECT(ans = allocVector(VECSXP, 9));
    for(int i = 0; i < 9; i++)
    SET_VECTOR_ELT(ans, i, allocVector(i > 0 ? INTSXP : REALSXP, n));

    PROTECT(ansnames = allocVector(STRSXP, 9));
    for(int i = 0; i < 9; i++)
    SET_STRING_ELT(ansnames, i, mkChar(ltnames[i]));

    for(R_xlen_t i = 0; i < n; i++) {
    if(R_FINITE(REAL(x)[i])) {
        day = (int) floor(REAL(x)[i]);
        tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
        /* weekday: 1970-01-01 was a Thursday */
        if ((tm.tm_wday = ((4 + day) % 7)) < 0) tm.tm_wday += 7;

        /* year & day within year */
        y = 1970;
        if (day >= 0)
        for ( ; day >= (tmp = days_in_year(y)); day -= tmp, y++);
        else
        for ( ; day < 0; --y, day += days_in_year(y) );

        y = tm.tm_year = y - 1900;
        tm.tm_yday = day;

        /* month within year */
        for (mon = 0;
         day >= (tmp = (days_in_month[mon]) +
             ((mon==1 && isleap(y+1900))?1:0));
         day -= tmp, mon++);
        tm.tm_mon = mon;
        tm.tm_mday = day + 1;
        tm.tm_isdst = 0; /* no dst in GMT */

        valid = 1;
    } else valid = 0;
    makelt(&tm, ans, i, valid, 0.0);
    }
    setAttrib(ans, R_NamesSymbol, ansnames);
    PROTECT(klass = allocVector(STRSXP, 2));
    SET_STRING_ELT(klass, 0, mkChar("POSIXlt"));
    SET_STRING_ELT(klass, 1, mkChar("POSIXt"));
    classgets(ans, klass);
    SEXP s_tzone = install("tzone");
    setAttrib(ans, s_tzone, mkString("UTC"));
    SEXP nm = getAttrib(x, R_NamesSymbol);
    if(! IS_R_NilValue(nm)) setAttrib(VECTOR_ELT(ans, 5), R_NamesSymbol, nm);
    UNPROTECT(4);

    return ans;
}

SEXP attribute_hidden do_POSIXlt2D(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP x, ans, klass;
    R_xlen_t n = 0, nlen[9];
    stm tm;

    checkArity(op, args);
    PROTECT(x = duplicate(CAR(args)));
    if(!isVectorList(x) || LENGTH(x) < 9)
    error(_("invalid '%s' argument"), "x");

    for(int i = 3; i < 6; i++)
    if((nlen[i] = XLENGTH(VECTOR_ELT(x, i))) > n) n = nlen[i];
    if((nlen[8] = XLENGTH(VECTOR_ELT(x, 8))) > n) n = nlen[8];
    if(n > 0) {
    for(int i = 3; i < 6; i++)
        if(nlen[i] == 0)
        error(_("zero-length component in non-empty \"POSIXlt\" structure"));
    if(nlen[8] == 0)
        error(_("zero-length component in non-empty \"POSIXlt\" structure"));
    }
    /* coerce relevant fields to integer */
    for(int i = 3; i < 6; i++)
    SET_VECTOR_ELT(x, i, coerceVector(VECTOR_ELT(x, i), INTSXP));

    PROTECT(ans = allocVector(REALSXP, n));
    for(R_xlen_t i = 0; i < n; i++) {
    tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
    tm.tm_mday  = INTEGER(VECTOR_ELT(x, 3))[i%nlen[3]];
    tm.tm_mon   = INTEGER(VECTOR_ELT(x, 4))[i%nlen[4]];
    tm.tm_year  = INTEGER(VECTOR_ELT(x, 5))[i%nlen[5]];
    /* mktime ignores tm.tm_wday and tm.tm_yday */
    tm.tm_isdst = 0;
    if(tm.tm_mday == NA_INTEGER || tm.tm_mon == NA_INTEGER ||
       tm.tm_year == NA_INTEGER || validate_tm(&tm) < 0)
        REAL(ans)[i] = NA_REAL;
    else {
        /* -1 must be error as seconds were zeroed */
        double tmp = mktime00(&tm);
        REAL(ans)[i] = (tmp == -1) ? NA_REAL : tmp/86400;
    }
    }

    PROTECT(klass = mkString("Date"));
    classgets(ans, klass);
    UNPROTECT(3);
    return ans;
}