ignore pre blocks

code.rb

@@ -1,4 +1,14 @@
+require 'digest/md5'
+
 def gfm(text)
+  # Extract pre blocks
+  extractions = {}
+  text.gsub!(%r{<pre>.*?</pre>}m) do |match|
+    md5 = Digest::MD5.hexdigest(match)
+    extractions[md5] = match
+    "{gfm-extraction-#{md5}}"
+  end
+
   # prevent foo_bar_baz from ending up with an italic word in the middle
   text.gsub!(/(^(?! {4}|\t)\w+_\w+_\w[\w_]*)/) do |x|
     x.gsub('_', '\_') if x.split('').sort.to_s[0..1] == '__'
@@ -9,6 +19,11 @@ def gfm(text)
     x.gsub(/^(.+)$/, "\\1  ")
   end
 
+  # Insert pre block extractions
+  text.gsub!(/\{gfm-extraction-([0-9a-f]{32})\}/) do
+    extractions[$1]
+  end
+
   text
 end
 
@@ -22,6 +37,14 @@ class GFMTest < Test::Unit::TestCase
         assert_equal "foo_bar", gfm("foo_bar")
       end
 
+      should "not touch underscores in code blocks" do
+        assert_equal "    foo_bar_baz", gfm("    foo_bar_baz")
+      end
+
+      should "not touch underscores in pre blocks" do
+        assert_equal "<pre>\nfoo_bar_baz\n</pre>", gfm("<pre>\nfoo_bar_baz\n</pre>")
+      end
+
       should "escape two or more underscores inside words" do
         assert_equal "foo\\_bar\\_baz", gfm("foo_bar_baz")
       end