merge revision(s) d6a2bce64a7fa1099e507e1d36b5f1533f42f60f,c687be4bc01c9ce52ea990945d9304d6fe59fe9b: [Backport #16159]

	time.c (find_time_t): fix round-to-zero bug

	`find_time_t` did not work correctly for year older than the Epoch
	because it used C's integer division (which rounds negative to zero).

	For example, `TIme.new(1933)` returned a wrong time whose year is 1922
	in Asia/Kuala_Lumpur because there is no 00:00:00 1st Jan. 1933 in the
	time zone.

	```
	$ TZ=Asia/Kuala_Lumpur ruby -e 'p Time.new(1933)'
	1932-12-31 00:00:00 +0700
	```

	This change fixes the issue by using `DIV` macro instead of `/`.
	Now `Time.new(1933)` returns a time in 1933.

	```
	$ TZ=Asia/Kuala_Lumpur ruby -e 'p Time.new(1933)'
	1933-01-01 00:20:00 +0720
	```

	[Bug #16159]

	Added a test for [Bug #16159]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67836 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 6 insertions, 6 deletions

diff --git a/time.c b/time.c
index 3bbfce6b38..75db5540c9 100644
--- a/time.c
+++ b/time.c
@@ -3273,12 +3273,12 @@ find_time_t(struct tm *tptr, int utc_p, time_t *tp)
 
     *tp = guess_lo +
           ((tptr->tm_year - tm_lo.tm_year) * 365 +
-           ((tptr->tm_year-69)/4) -
-           ((tptr->tm_year-1)/100) +
-           ((tptr->tm_year+299)/400) -
-           ((tm_lo.tm_year-69)/4) +
-           ((tm_lo.tm_year-1)/100) -
-           ((tm_lo.tm_year+299)/400) +
+           DIV((tptr->tm_year-69), 4) -
+           DIV((tptr->tm_year-1), 100) +
+           DIV((tptr->tm_year+299), 400) -
+           DIV((tm_lo.tm_year-69), 4) +
+           DIV((tm_lo.tm_year-1), 100) -
+           DIV((tm_lo.tm_year+299), 400) +
            tptr_tm_yday -
            tm_lo.tm_yday) * 86400 +
           (tptr->tm_hour - tm_lo.tm_hour) * 3600 +