static struct dt_ddur_s
__ymcw_diff(dt_ymcw_t d1, dt_ymcw_t d2)
{
/* compute d2 - d1 entirely in terms of ymd */
struct dt_ddur_s res = dt_make_ddur(DT_DURYMCW, 0);
signed int tgtd;
signed int tgtm;
dt_dow_t wd01, wd02;
if (__ymcw_cmp(d1, d2) > 0) {
dt_ymcw_t tmp = d1;
d1 = d2;
d2 = tmp;
res.neg = 1;
}
wd01 = __get_m01_wday(d1.y, d1.m);
if (d2.y != d1.y || d2.m != d1.m) {
wd02 = __get_m01_wday(d2.y, d2.m);
} else {
wd02 = wd01;
}
/* first compute the difference in months Y2-M2-01 - Y1-M1-01 */
tgtm = GREG_MONTHS_P_YEAR * (d2.y - d1.y) + (d2.m - d1.m);
/* using the firsts of the month WD01, represent d1 and d2 as
* the C-th WD01 plus OFF */
{
unsigned int off1;
unsigned int off2;
off1 = __uimod(d1.w - wd01, GREG_DAYS_P_WEEK);
off2 = __uimod(d2.w - wd02, GREG_DAYS_P_WEEK);
tgtd = off2 - off1 + GREG_DAYS_P_WEEK * (d2.c - d1.c);
}
/* fixups */
if (tgtd < (signed int)GREG_DAYS_P_WEEK && tgtm > 0) {
/* if tgtm is 0 it remains 0 and tgtd remains negative */
/* get the target month's mdays */
unsigned int d2m = d2.m;
unsigned int d2y = d2.y;
if (--d2m < 1) {
d2m = GREG_MONTHS_P_YEAR;
d2y--;
}
tgtd += __get_mdays(d2y, d2m);
tgtm--;
}
/* fill in the results */
res.ymcw.y = tgtm / GREG_MONTHS_P_YEAR;
res.ymcw.m = tgtm % GREG_MONTHS_P_YEAR;
res.ymcw.c = tgtd / GREG_DAYS_P_WEEK;
res.ymcw.w = tgtd % GREG_DAYS_P_WEEK;
return res;
}
DEFUN unsigned int
__get_bdays(unsigned int y, unsigned int m)
{
/* the 28th exists in every month, and it's exactly 20 bdays
* away from the first, oh and it's -1 mod 7
* then to get the number of bdays remaining in the month
* from the number of days remaining in the month R
* we use a multiplication table, downwards the weekday of the
* 28th, rightwards the days in excess of the 28th
* Miracleday is only there to make the left hand side of the
* multiplication 3 bits wide:
*
* r-> 0 1 2 3
* Sun 0 1 2 3
* Mon 0 1 2 3
* Tue 0 1 2 3
* Wed 0 1 2 2
* Thu 0 1 1 1
* Fri 0 0 0 1
* Sat 0 0 1 2
* Mir 0 0 0 0
*/
unsigned int md = __get_mdays(y, m);
unsigned int rd = (unsigned int)(md - 28U);
dt_dow_t m01wd;
unsigned int m28wd;
/* rd should not overflow */
assert((signed int)md - 28 >= 0);
/* wday of the 1st and 28th */
m01wd = __get_m01_wday(y, m);
m28wd = __uimod((signed int)m01wd - 1, GREG_DAYS_P_WEEK);
if (LIKELY(rd > 0)) {
switch ((dt_dow_t)m28wd) {
case DT_SUNDAY:
case DT_MONDAY:
case DT_TUESDAY:
return 20 + rd;
case DT_WEDNESDAY:
return 20 + rd - (rd == 3);
case DT_THURSDAY:
return 21;
case DT_FRIDAY:
return 20 + (rd == 3);
case DT_SATURDAY:
return 20 + rd - 1;
case DT_MIRACLEDAY:
default:
abort();
}
}
return 20U;
}
DEFUN int
__ymcw_cmp(dt_ymcw_t d1, dt_ymcw_t d2)
{
if (d1.y < d2.y) {
return -1;
} else if (d1.y > d2.y) {
return 1;
} else if (d1.m < d2.m) {
return -1;
} else if (d1.m > d2.m) {
return 1;
}
/* we're down to counts, however, the last W of a month is always
* count 5, even though counting forward it would be 4 */
if (d1.c < d2.c) {
return -1;
} else if (d1.c > d2.c) {
return 1;
}
/* now it's up to the first of the month */
{
dt_dow_t wd01;
unsigned int off1;
unsigned int off2;
wd01 = __get_m01_wday(d1.y, d1.m);
/* represent cw as C-th WD01 + OFF */
off1 = __uimod(d1.w - wd01, GREG_DAYS_P_WEEK);
off2 = __uimod(d2.w - wd01, GREG_DAYS_P_WEEK);
if (off1 < off2) {
return -1;
} else if (off1 > off2) {
return 1;
} else {
return 0;
}
}
}
