change.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>

static void make_incr();


int datetime_change_from_to(DateTime * dt, int from, int to, int round)
{
    DateTime dummy, incr;
    int pos;
    int carry;
    int ndays;
    int dtfrom;

    /* is 'dt' valid? */
    if (!datetime_is_valid_type(dt))
        return -1;

    /* is new from/to valid for dt->mode? */
    if (datetime_set_type(&dummy, dt->mode, from, to, 0) != 0)
        return -2;

    /* copy dt->from to local variable, then change it
       in the structure so that increment works correctly for RELATIVE.
       Otherwise, since increment "reduces" answers, performing carries, 
       we would carry to invalid units */

    dtfrom = dt->from;

    /* now set the from */
    dt->from = from;

    /* convert the "lost" lower elements to equiv value for the new 'from'
     * NOTE: this only affects DATETIME_RELATIVE 
     *       since absolute will have from==dt->from==YEAR
     */
    for (pos = dtfrom; pos < from; pos++) {
        switch (pos) {
        case DATETIME_YEAR:
            dt->month += dt->year * 12;
            dt->year = 0;
            break;
        case DATETIME_DAY:
            dt->hour += dt->day * 24;
            dt->day = 0;
            break;
        case DATETIME_HOUR:
            dt->minute += dt->hour * 60;
            dt->hour = 0;
            break;
        case DATETIME_MINUTE:
            dt->second += dt->minute * 60.0;
            dt->minute = 0;
            break;
        }
    }

    /* if losing precision, round
     *    round > 0 force up if any lost values not zero
     *    round ==0 increment by all lost values
     */
    if (to < dt->to) {
        if (round > 0) {
            int x;

            x = datetime_is_absolute(dt) ? 1 : 0;

            for (carry = 0, pos = dt->to; carry == 0 && pos > to; pos--) {
                switch (pos) {
                case DATETIME_MONTH:
                    if (dt->month != x)
                        carry = 1;
                    break;
                case DATETIME_DAY:
                    if (dt->day != x)
                        carry = 1;
                    break;
                case DATETIME_HOUR:
                    if (dt->hour != 0)
                        carry = 1;
                    break;
                case DATETIME_MINUTE:
                    if (dt->minute != 0)
                        carry = 1;
                    break;
                case DATETIME_SECOND:
                    if (dt->second != 0)
                        carry = 1;
                    break;
                }
            }

            if (carry) {
                make_incr(&incr, to, to, dt);

                incr.year = 1;
                incr.month = 1;
                incr.day = 1;
                incr.hour = 1;
                incr.minute = 1;
                incr.second = 1.0;

                datetime_increment(dt, &incr);
            }
        }

        if (round == 0) {
             /*NEW*/ if (datetime_is_absolute(dt))
                /*NEW*/ ndays = datetime_days_in_year(dt->year, dt->positive);
             /*NEW*/
            else
                /*NEW*/ ndays = 0;

            for (pos = dt->to; pos > to; pos--) {
                make_incr(&incr, pos, pos, dt);

                incr.year = dt->year;
                incr.month = dt->month;
                 /*NEW*/ incr.day = dt->day + ndays / 2;
                incr.hour = dt->hour;
                incr.minute = dt->minute;
                incr.second = dt->second;

                datetime_increment(dt, &incr);
                 /*NEW*/ if (ndays > 0 && pos == DATETIME_DAY)
                    /*NEW*/ break;
            }
        }
    }

    /* set the new elements to zero */
    for (pos = from; pos < dtfrom; pos++)
        switch (pos) {
        case DATETIME_YEAR:
            dt->year = 0;
            break;
        case DATETIME_MONTH:
            dt->month = 0;
            break;
        case DATETIME_DAY:
            dt->day = 0;
            break;
        case DATETIME_HOUR:
            dt->hour = 0;
            break;
        case DATETIME_MINUTE:
            dt->minute = 0;
            break;
        case DATETIME_SECOND:
            dt->second = 0;
            break;
        }

    for (pos = to; pos > dt->to; pos--)
        switch (pos) {
        case DATETIME_YEAR:
            dt->year = 0;
            break;
        case DATETIME_MONTH:
            dt->month = 0;
            break;
        case DATETIME_DAY:
            dt->day = 0;
            break;
        case DATETIME_HOUR:
            dt->hour = 0;
            break;
        case DATETIME_MINUTE:
            dt->minute = 0;
            break;
        case DATETIME_SECOND:
            dt->second = 0;
            break;
        }

    /* make sure that fracsec is zero if original didn't have seconds */
    if (dt->to < DATETIME_SECOND)
        dt->fracsec = 0;

    /* now set the to */
    dt->to = to;

    return 0;
}

static void make_incr(DateTime * incr, int from, int to, DateTime * dt)
{
    datetime_set_type(incr, DATETIME_RELATIVE, from, to, 0);
    if (datetime_is_relative(dt) && datetime_is_negative(dt))
        datetime_set_negative(incr);
}