From c5ff6a7461a63af9174e0ea70d0bc4a7b1b1c7cf Mon Sep 17 00:00:00 2001
From: Davis King <davis@dlib.net>
Date: Mon, 17 Mar 2014 18:00:44 -0400
Subject: [PATCH] Improved speed of reshape_to_column_vector()

---
 dlib/matrix/matrix_utilities.h | 45 ++++++++++++++++++++++++++++++++++
 dlib/test/matrix3.cpp          |  2 ++
 2 files changed, 47 insertions(+)

diff --git a/dlib/matrix/matrix_utilities.h b/dlib/matrix/matrix_utilities.h
index 107f21bca..3b6108cc2 100644
--- a/dlib/matrix/matrix_utilities.h
+++ b/dlib/matrix/matrix_utilities.h
@@ -3901,6 +3901,51 @@ namespace dlib
         return matrix_op<op>(op(m.ref()));
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename T,
+        long NR_,
+        long NC_,
+        typename MM
+        >
+    struct op_mat_to_vect2
+    {
+        typedef matrix<T,NR_,NC_,MM,row_major_layout> M;
+        op_mat_to_vect2(const M& m_) : m(m_) {}
+        const M& m;
+
+        const static long cost = M::cost+2;
+        const static long NR = M::NC*M::NR;
+        const static long NC = 1;
+        typedef typename M::type type;
+        typedef typename M::const_ret_type const_ret_type;
+        typedef typename M::mem_manager_type mem_manager_type;
+        typedef typename M::layout_type layout_type;
+
+        const_ret_type apply ( long r, long ) const { return (&m(0,0))[r]; }
+
+        long nr () const { return m.size(); }
+        long nc () const { return 1; }
+
+        template <typename U> bool aliases               ( const matrix_exp<U>& item) const { return m.aliases(item); }
+        template <typename U> bool destructively_aliases ( const matrix_exp<U>& item) const { return m.aliases(item); }
+    }; 
+
+    template <
+        typename T,
+        long NR,
+        long NC,
+        typename MM
+        >
+    const matrix_op<op_mat_to_vect2<T,NR,NC,MM> > reshape_to_column_vector (
+        const matrix<T,NR,NC,MM,row_major_layout>& m
+    )
+    {
+        typedef op_mat_to_vect2<T,NR,NC,MM> op;
+        return matrix_op<op>(op(m.ref()));
+    }
+
 // ----------------------------------------------------------------------------------------
 
     template <typename M1, typename M2>
diff --git a/dlib/test/matrix3.cpp b/dlib/test/matrix3.cpp
index 15847ab80..46dde12a9 100644
--- a/dlib/test/matrix3.cpp
+++ b/dlib/test/matrix3.cpp
@@ -610,6 +610,7 @@ namespace
             m2 = 1,2,3,4,5,6;
 
             DLIB_TEST(reshape_to_column_vector(m) == m2);
+            DLIB_TEST(reshape_to_column_vector(m+m) == m2+m2);
 
         }
         {
@@ -622,6 +623,7 @@ namespace
             m2 = 1,2,3,4,5,6;
 
             DLIB_TEST(reshape_to_column_vector(m) == m2);
+            DLIB_TEST(reshape_to_column_vector(m+m) == m2+m2);
 
         }
     }