From 475b97464dae806d547e8bf9fb3adf78bcf8d86f Mon Sep 17 00:00:00 2001
From: conrad <conrad@localhost.localdomain>
Date: Mon, 20 Oct 2025 12:21:33 +1000
Subject: [PATCH] faster handling of row subvectors

---
 include/armadillo_bits/Row_bones.hpp |  3 +++
 include/armadillo_bits/Row_meat.hpp  | 18 ++++++++++++++++++
 include/armadillo_bits/unwrap.hpp    | 24 ++++++++++++++----------
 3 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/include/armadillo_bits/Row_bones.hpp b/include/armadillo_bits/Row_bones.hpp
index dfcb1b29..fdb9612f 100644
--- a/include/armadillo_bits/Row_bones.hpp
+++ b/include/armadillo_bits/Row_bones.hpp
@@ -169,6 +169,9 @@ class Row : public Mat<eT>
   inline const_row_iterator end_row  (const uword row_num) const;
   
   
+  inline explicit Row(const subview<eT>& X, const bool reuse_mem);  // only to be used by the partial_unwrap class
+  
+  
   template<uword fixed_n_elem> class fixed;
   
   
diff --git a/include/armadillo_bits/Row_meat.hpp b/include/armadillo_bits/Row_meat.hpp
index 4851e987..987a0f48 100644
--- a/include/armadillo_bits/Row_meat.hpp
+++ b/include/armadillo_bits/Row_meat.hpp
@@ -1264,6 +1264,20 @@ Row<eT>::end_row(const uword row_num) const
 
 
 
+template<typename eT>
+inline
+Row<eT>::Row(const subview<eT>& X, const bool reuse_mem)
+  : Mat<eT>(X, reuse_mem)
+  {
+  arma_debug_sigprint_this(this);
+  }
+
+
+
+//
+
+
+
 template<typename eT>
 template<uword fixed_n_elem>
 arma_inline
@@ -1859,6 +1873,10 @@ Row<eT>::fixed<fixed_n_elem>::ones()
 
 
 
+//
+
+
+
 template<typename eT>
 inline
 Row<eT>::Row(const arma_fixed_indicator&, const uword in_n_elem, const eT* in_mem)
diff --git a/include/armadillo_bits/unwrap.hpp b/include/armadillo_bits/unwrap.hpp
index 07d581c0..4d64744a 100644
--- a/include/armadillo_bits/unwrap.hpp
+++ b/include/armadillo_bits/unwrap.hpp
@@ -382,19 +382,21 @@ struct quasi_unwrap< subview_row<eT> >
   {
   inline
   quasi_unwrap(const subview_row<eT>& A)
-    : M(A)
+    : sv( A                    )
+    , M ( A, (A.m.n_rows == 1) )
     {
     arma_debug_sigprint();
     }
   
-  Row<eT> M;
+  const subview_row<eT>& sv;
+  const Row<eT>          M;
   
-  static constexpr bool is_const     = false;
-  static constexpr bool has_subview  = false;
-  static constexpr bool has_orig_mem = false;
+  static constexpr bool is_const     = true;
+  static constexpr bool has_subview  = true;
+  static constexpr bool has_orig_mem = false;  // NOTE: set to false as this is the general case; original memory is only used when the subview is a contiguous chunk
   
   template<typename eT2>
-  constexpr bool is_alias(const Mat<eT2>&) const { return false; }
+  arma_inline bool is_alias(const Mat<eT2>& X) const { return (is_same_type<eT,eT2>::yes) && ( (sv.m.n_rows == 1) ? (void_ptr(&X) == void_ptr(&(sv.m))) : false ); }
   };
 
 
@@ -1430,7 +1432,8 @@ struct partial_unwrap< subview_row<eT> >
   
   inline
   partial_unwrap(const subview_row<eT>& A)
-    : M(A)
+    : sv( A                    )
+    , M ( A, (A.m.n_rows == 1) )
     {
     arma_debug_sigprint();
     }
@@ -1438,13 +1441,14 @@ struct partial_unwrap< subview_row<eT> >
   constexpr eT get_val() const { return eT(1); }
   
   template<typename eT2>
-  constexpr bool is_alias(const Mat<eT2>&) const { return false; }
+  arma_inline bool is_alias(const Mat<eT2>& X) const { return (sv.m.n_rows == 1) ? (void_ptr(&X) == void_ptr(&(sv.m))) : false; }
   
   static constexpr bool do_trans = false;
   static constexpr bool do_times = false;
-  static constexpr bool is_fast  = false;
+  static constexpr bool is_fast  = false;  // can't determine at compile time that memory is reused
   
-  const Row<eT> M;
+  const subview_row<eT>& sv;
+  const Row<eT>          M;
   };