src/lib/utc-offset.c

/* Copyright (c) 2002-2018 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "utc-offset.h"

#include <sys/time.h>

int utc_offset(struct tm *tm, time_t t ATTR_UNUSED)
{
#ifdef HAVE_TM_GMTOFF
    return (int) (tm->tm_gmtoff/60);
#else
    struct tm ltm, gtm;
    int offset;

    /* gmtime() overwrites tm, so we need to copy it elsewhere */
    ltm = *tm;
    tm = gmtime(&t);
    gtm = *tm;

    /* max offset of 24 hours */
    if ((ltm.tm_yday < gtm.tm_yday && ltm.tm_year == gtm.tm_year) ||
        ltm.tm_year < gtm.tm_year)
        offset = -24 * 60;
    else if ((ltm.tm_yday > gtm.tm_yday && ltm.tm_year == gtm.tm_year) ||
         ltm.tm_year > gtm.tm_year)
        offset = 24 * 60;
    else
        offset = 0;

    offset += (ltm.tm_hour - gtm.tm_hour) * 60;
    offset += (ltm.tm_min - gtm.tm_min);

    /* restore overwritten tm */
    *tm = ltm;
    return offset;
#endif
}