Re: Re[2]: [Dev-C++] OT: week number

[Per W. <pw...@ia...>]

A nice program should check which day is first of week in current locale.
Here is code updated with such check:

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>

#define ALLOW_S2_LESS_THAN_S1

bool is_same_week(SYSTEMTIME& s1,SYSTEMTIME& s2) {
    TCHAR buf[2];
    FILETIME f1,f2;
    ULARGE_INTEGER u1,u2;
#ifdef ALLOW_S2_LESS_THAN_S1
    ULONGLONG tmp;
#endif
    int size,firstday,wday1,wday2;

    /* Check which weekday that starts the week. 0=monday */
    size = GetLocaleInfo(LOCALE_USER_DEFAULT,
                         LOCALE_IFIRSTDAYOFWEEK,buf,2);
    firstday = size==0 ? 6 : atoi(buf);
    printf("First day of week is %d (0=monday)\n",firstday);

    /* Adjust the weekdays given in the SYSTEMTIME struct (0=sunday)
     * so that the first day of the week according to locale
     * becomes 0.
     */
    wday1 = (s1.wDayOfWeek + (6 - firstday)) % 7;
    wday2 = (s2.wDayOfWeek + (6 - firstday)) % 7;

    printf("w1 = %d (%d)\n",wday1,s1.wDayOfWeek);
    printf("w2 = %d (%d)\n",wday2,s2.wDayOfWeek);

#ifndef ALLOW_S2_LESS_THAN_S1
    if (wday2 < wday1)
        /* Given the assumption that s2 must be larger than s1,
         * they can't be in same week unless s2 has weekday
         * >= s1.
         */
        return false;
#endif /* ALLOW_S2_LESS_THAN_S1 */

    /* Convert from SYSTEMTIME to a single numeric value */
    SystemTimeToFileTime(&s1,&f1);
    SystemTimeToFileTime(&s2,&f2);
    u1.LowPart = f1.dwLowDateTime;
    u1.HighPart = f1.dwHighDateTime;
    u2.LowPart = f2.dwLowDateTime;
    u2.HighPart = f2.dwHighDateTime;
    /* Now have time in 100-nanosecond steps */

#ifdef ALLOW_S2_LESS_THAN_S1
    /* if s1 <= s2 isn't a requirement then have to check if the two
     * values must be swapped.
     */
    if (u1.QuadPart < u2.QuadPart) {
        if (wday2 < wday1) return false;
    } else {
        if (wday1 < wday2) return false;
        tmp = u1.QuadPart;
        u1.QuadPart = u2.QuadPart;
        u2.QuadPart = tmp;
    }
#else
    if (u2.QuadPart < u1.QuadPart)
        /* End of time interval before start... */
        return false;
#endif /* !ALLOW_S2_LESS_THAN_S1 */

    if (u2.QuadPart > (u1.QuadPart + 7*24*3600*(ULONGLONG)10000000))
        /* more than 7 days between the two time stamps, so they can't
         * be in same week.
         */
        return false;

    return true;
}

/Per W