tz2.c

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/*
 * Copyright (C) 1995.  Bill Brown <brown@gis.uiuc.edu> & Michael Shapiro
 *
 * This program is free software under the GPL (>=v2)
 * Read the file GPL.TXT coming with GRASS for details.
 */
#include <grass/datetime.h>


int datetime_change_timezone(DateTime * dt, int minutes)
{                               /* new timezone in minutes */
    int stat;
    int old_minutes, diff_minutes;
    DateTime incr;

    stat = datetime_get_timezone(dt, &old_minutes);
    if (stat != 0)
        return stat;
    if (!datetime_is_valid_timezone(minutes))
        return datetime_error(-4, "invalid datetime timezone");

    /* create a relative minute increment */
    datetime_set_type(&incr, DATETIME_RELATIVE, DATETIME_MINUTE,
                      DATETIME_MINUTE, 0);

    /* BB - needed to set SIGN here */
    diff_minutes = minutes - old_minutes;
    if (diff_minutes >= 0) {
        datetime_set_minute(&incr, diff_minutes);
    }
    else {
        datetime_invert_sign(&incr);
        datetime_set_minute(&incr, -diff_minutes);
    }

    return datetime_increment(dt, &incr);
}


int datetime_change_to_utc(DateTime * dt)
{
    return datetime_change_timezone(dt, 0);
}


void datetime_decompose_timezone(int tz, int *hours, int *minutes)
{
    if (tz < 0)
        tz = -tz;

    *hours = tz / 60;
    *minutes = tz % 60;
}