[search] Performance: Avoid penalty on polymorphic SubReader and coping of readers.

1 files changed, 35 insertions, 0 deletions

diff --git a/coding/reader_wrapper.hpp b/coding/reader_wrapper.hpp
new file mode 100644
index 0000000000..e45b940e9e
--- /dev/null
+++ b/coding/reader_wrapper.hpp
@@ -0,0 +1,35 @@
+#pragma once
+
+#include "../base/assert.hpp"
+
+
+/// Reader wrapper to avoid penalty on copy and polymorphic SubReader creation.
+template <class ReaderT> class SubReaderWrapper
+{
+  ReaderT * m_p;
+  uint64_t m_pos;
+  uint64_t m_size;
+
+protected:
+  SubReaderWrapper(ReaderT * p, uint64_t pos, uint64_t size)
+    : m_p(p), m_pos(pos), m_size(size)
+  {
+    ASSERT_LESS_OR_EQUAL ( pos + size, m_p->Size(), (pos, size) );
+  }
+
+public:
+  explicit SubReaderWrapper(ReaderT * p) : m_p(p), m_pos(0), m_size(p->Size()) {}
+
+  uint64_t Size() const { return m_size; }
+
+  void Read(uint64_t pos, void * p, size_t size) const
+  {
+    ASSERT_LESS_OR_EQUAL ( pos + size, m_size, (pos, size) );
+    m_p->Read(pos + m_pos, p, size);
+  }
+
+  SubReaderWrapper SubReader(uint64_t pos, uint64_t size) const
+  {
+    return SubReaderWrapper(m_p, pos + m_pos, size);
+  }
+};