add Buffer::Iterator::warp_to_offset()

src/core/Buffer-Iterator.cc

@@ -180,3 +180,24 @@ bool Buffer::Iterator::go_next_line()
     }
     return false;
 }
+
+void Buffer::Iterator::warp_to_offset(size_t offset)
+{
+    Iterator i = m_buffer->begin();
+    m_offset = i.m_offset;
+    m_line = i.m_line;
+    for (;;)
+    {
+        i.go_forward();
+        if (i.m_offset > offset)
+        {
+            break;
+        }
+        m_offset = i.m_offset;
+        m_line = i.m_line;
+        if (!i.valid())
+        {
+            break;
+        }
+    }
+}

src/core/Buffer.h

@@ -46,6 +46,7 @@ public:
             m_offset += offset_offset;
             m_line += line_offset;
         }
+        void warp_to_offset(size_t offset);
         uint8_t * address() const
         {
             return m_buffer->address(m_offset);