Add rw_ops::Reverse.

1 files changed, 27 insertions, 0 deletions

diff --git a/coding/reader_writer_ops.cpp b/coding/reader_writer_ops.cpp
new file mode 100644
index 0000000000..93dff6e8f4
--- /dev/null
+++ b/coding/reader_writer_ops.cpp
@@ -0,0 +1,27 @@
+#include "reader_writer_ops.hpp"
+
+namespace rw_ops
+{
+  void Reverse(Reader const & src, Writer & dest)
+  {
+    // Read from end, reverse and write directly.
+
+    size_t const bufSz = 1024;
+    vector<char> buffer(bufSz);
+
+    uint64_t pos = src.Size();
+    while (pos > 0)
+    {
+      size_t const sz = pos > bufSz ? bufSz : pos;
+      ASSERT_GREATER_OR_EQUAL(pos, sz, ());
+
+      src.Read(pos - sz, &buffer[0], sz);
+
+      std::reverse(buffer.begin(), buffer.begin() + sz);
+
+      dest.Write(&buffer[0], sz);
+
+      pos -= sz;
+    }
+  }
+}