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

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`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]
This commit is contained in:
Yusuke Endoh 2019-12-17 10:31:20 +09:00
parent 5da4a310cc
commit d6a2bce64a
1 changed files with 6 additions and 6 deletions
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12
time.c
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@ -3365,12 +3365,12 @@ 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 +