Repo created

libs/coding/reader_wrapper.hpp

@@ -0,0 +1,42 @@
+#pragma once
+
+#include "coding/reader.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); }
+};
+
+/// Non template reader source for regular functions with incapsulated implementation.
+class ReaderSrc : public ReaderSource<SubReaderWrapper<Reader>>
+{
+  typedef SubReaderWrapper<Reader> ReaderT;
+  typedef ReaderSource<ReaderT> BaseT;
+
+public:
+  explicit ReaderSrc(Reader & reader) : BaseT(ReaderT(&reader)) {}
+  explicit ReaderSrc(Reader * reader) : BaseT(ReaderT(reader)) {}
+};