Merge pull request #84 from mreinsch/month-subtraction-fix

fix for month subtraction
floraison · Jan 19, 2023 · 8072982 · 8072982
2 parents 9b1c6b1 + 88d0a6d
commit 8072982
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diff --git a/lib/fugit/duration.rb b/lib/fugit/duration.rb
@@ -240,7 +240,7 @@ def add_to_time(t)
           n, m = at[1] / 12, at[1] % 12
           at[0], at[1] = at[0] + n, m
         elsif at[1] < 1
-          n, m = -at[1] / 12, -at[1] % 12
+          n, m = (-at[1]) / 12 + 1, (11+at[1]) % 12 + 1
           at[0], at[1] = at[0] - n, m
         end
 

diff --git a/spec/duration_spec.rb b/spec/duration_spec.rb
@@ -385,6 +385,8 @@
       [ '1Y1m17s', '2016-12-30 17:00:00', '2017-12-30 17:01:17' ],
       [ '1Y1M17s', '2016-12-30 17:00:00', '2018-01-30 17:00:17' ],
       [ '1M', '2016-02-02', '2016-03-02' ],
+      [ '-2M', '2016-02-02', '2015-12-02' ],
+      [ '-15M', '2016-02-02', '2014-11-02' ],
     ].each do |d, t, tt|
 
       it "adding #{t.inspect} to #{d.inspect} yields #{tt.inspect}" do