add PieceTable::get_start_of_line()

src/core/PieceTable.cc

@@ -29,3 +29,15 @@ void PieceTable::append_initial_line_piece(uint8_t * start, uint32_t length, uin
     if (cursor_position.pd == end_descriptor)
         cursor_position.pd = pd;
 }
+
+PieceTable::PieceDescriptor * PieceTable::get_start_of_line(PieceTable::PieceDescriptor * start) const
+{
+    PieceDescriptor * pd = start;
+
+    while (pd->prev != start_descriptor && !pd->prev->eol())
+    {
+        pd = pd->prev;
+    }
+
+    return pd;
+}

src/core/PieceTable.h

@@ -81,6 +81,8 @@ public:
 
     void append_initial_line_piece(uint8_t * start, uint32_t length, uint32_t n_chars, bool eol);
 
+    PieceDescriptor * get_start_of_line(PieceDescriptor * start) const;
+
 protected:
     const uint8_t * m_file_buffer;
     unsigned long m_file_buffer_size;