Implement GapBuffer::Iterator movement functions

src/core/GapBuffer.cc

@@ -30,3 +30,29 @@ std::shared_ptr<GapBuffer::Cursor> GapBuffer::add_cursor()
     m_cursors.push_back(cursor);
     return cursor;
 }
+
+
+void GapBuffer::Iterator::forward()
+{
+    if (valid())
+    {
+        m_offset += Encoding::num_bytes_in_code_point(m_gap_buffer->m_encoding, address());
+    }
+}
+
+void GapBuffer::Iterator::back()
+{
+    if (valid())
+    {
+        if (m_offset == 0u)
+        {
+            m_offset = 0xFFFFFFFFu;
+        }
+        else
+        {
+            const uint8_t * a = m_gap_buffer->address(m_offset - 1u);
+            const uint8_t * beginning_of_code_point = Encoding::beginning_of_code_point(m_gap_buffer->m_encoding, a);
+            m_offset -= ((a - beginning_of_code_point) + 1u);
+        }
+    }
+}

src/core/GapBuffer.h

@@ -18,10 +18,16 @@ public:
             m_gap_buffer = gap_buffer;
             m_offset = 0u;
         }
-        bool valid()
+        bool valid() const
         {
             return m_offset < m_gap_buffer->size();
         }
+        void forward();
+        void back();
+        uint8_t * address() const
+        {
+            return m_gap_buffer->address(m_offset);
+        }
 
     protected:
         GapBuffer * m_gap_buffer;
@@ -47,9 +53,20 @@ public:
     GapBuffer(Encoding::Type encoding);
     GapBuffer(uint8_t * buffer, size_t buffer_size, size_t size, Encoding::Type encoding);
     ~GapBuffer();
-    size_t buffer_size() { return m_buffer_size; }
-    size_t size() { return m_size; }
+    size_t buffer_size() const { return m_buffer_size; }
+    size_t size() const { return m_size; }
     std::shared_ptr<Cursor> add_cursor();
+    uint8_t * address(size_t offset) const
+    {
+        if (offset < m_gap_position)
+        {
+            return &m_buffer[offset];
+        }
+        else
+        {
+            return &m_buffer[offset + (m_buffer_size - m_size)];
+        }
+    }
 
 protected:
     uint8_t * m_buffer;