[ruby-cvs:78760] 650c45dcd7 (ruby_2_6): merge revision(s) d6a2bce64a7fa1099e507e1d36b5f1533f42f60f,c687be4bc01c9ce52ea 990945d9304d6fe59fe9b: [Backport #16159]

nagachika	2019-12-18 22:41:48 +0900 (Wed, 18 Dec 2019)

  New Revision: 650c45dcd7

  https://github.com/ruby/ruby/commit/650c45dcd7

  Log:
    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

  Modified files:
    test/ruby/test_time_tz.rb
    time.c
    version.h