add a gap position to GapBuffer

src/core/GapBuffer.cc

@@ -6,6 +6,7 @@ GapBuffer::GapBuffer()
     m_buffer = (uint8_t *)System::alloc_pages(1u);
     m_buffer_size = System::page_size;
     m_size = 0u;
+    m_gap_position = 0u;
 }
 
 GapBuffer::GapBuffer(uint8_t * buffer, size_t buffer_size, size_t size)
@@ -13,6 +14,7 @@ GapBuffer::GapBuffer(uint8_t * buffer, size_t buffer_size, size_t size)
     m_buffer = buffer;
     m_buffer_size = buffer_size;
     m_size = size;
+    m_gap_position = size;
 }
 
 GapBuffer::~GapBuffer()

src/core/GapBuffer.h

@@ -15,6 +15,7 @@ protected:
     uint8_t * m_buffer;
     size_t m_buffer_size;
     size_t m_size;
+    size_t m_gap_position;
 };
 
 #endif