Merge pull request #18 from pck/fix_prune_common_start

Fix pruning of common sequences at start.

2 files changed, 7 insertions, 0 deletions

diff --git a/lib/diff/lcs/internals.rb b/lib/diff/lcs/internals.rb
index fe4ed9b..9d9e3f3 100644
--- a/lib/diff/lcs/internals.rb
+++ b/lib/diff/lcs/internals.rb
@@ -49,6 +49,7 @@ class << Diff::LCS::Internals
            (a[a_start] == b[b_start]))
       vector[a_start] = b_start
       a_start += 1
+      b_start += 1
     end
     b_start = a_start
 
diff --git a/spec/diff_spec.rb b/spec/diff_spec.rb
index e82ab3d..95d7b40 100644
--- a/spec/diff_spec.rb
+++ b/spec/diff_spec.rb
@@ -31,6 +31,12 @@ describe "Diff::LCS.diff" do
     change_diff(correct_diff).should == diff
   end
 
+  it "should correctly diff 'xx' and 'xaxb'" do
+    left = 'xx'
+    right = 'xaxb'
+    Diff::LCS.patch(left, Diff::LCS.diff(left, right)).should == right
+  end
+
   it "should return an empty diff with (hello, hello)" do
     Diff::LCS.diff(hello, hello).should == []
   end