From f2d0ad999e547a478c23dc38a8f6f484541cdbd9 Mon Sep 17 00:00:00 2001
From: Alexey Kopytko <alexey@kopytko.ru>
Date: Wed, 21 Dec 2016 14:04:56 +0900
Subject: [PATCH] rndr_header_anchor: use djb2 hash for non-ascii text

---
 ext/redcarpet/html.c     | 9 +++++++++
 test/html_render_test.rb | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/ext/redcarpet/html.c b/ext/redcarpet/html.c
index 2f717ba6..9eab059d 100644
--- a/ext/redcarpet/html.c
+++ b/ext/redcarpet/html.c
@@ -307,6 +307,15 @@ rndr_header_anchor(struct buf *out, const struct buf *anchor)
 	// replace the last dash if there was anything added
 	if (stripped && inserted)
 		out->size--;
+
+	// if anchor found empty, use djb2 hash for it
+	if (!inserted && anchor->size) {
+	        unsigned long hash = 5381;
+		for (i = 0; i < size; ++i) {
+			hash = ((hash << 5) + hash) + a[i]; /* h * 33 + c */
+		}
+		bufprintf(out, "part-%lx", hash);
+	}
 }
 
 static void
diff --git a/test/html_render_test.rb b/test/html_render_test.rb
index 9bc3da95..3fdd2ca5 100644
--- a/test/html_render_test.rb
+++ b/test/html_render_test.rb
@@ -254,7 +254,7 @@ def test_non_ascii_removal_in_header_anchors
 
   def test_utf8_only_header_anchors
     markdown = "# 見出し"
-    html = "<h1 id=\"\">見出し</h1>"
+    html = "<h1 id=\"part-37870bfa194139f\">見出し</h1>"
 
     assert_equal html, render(markdown, with: [:with_toc_data])
   end