From 3baced9adbf25bedf034eef4fab74a12e32b575a Mon Sep 17 00:00:00 2001
From: Jiri Pittner <jiri@pittnerovi.com>
Date: Thu, 23 Oct 2025 16:15:42 +0200
Subject: [PATCH] const version of loopover and grouploopoevr in tensor class

---
 tensor.cc | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
 tensor.h  |  4 +--
 2 files changed, 94 insertions(+), 7 deletions(-)

diff --git a/tensor.cc b/tensor.cc
index 1314923..16ab17a 100644
--- a/tensor.cc
+++ b/tensor.cc
@@ -376,6 +376,7 @@ calcsize();
 }
 
 
+
 template<typename T>
 void loopingroups(Tensor<T> &t, int ngroup, int igroup, T **p, SUPERINDEX &I, void (*callback)(const SUPERINDEX &, T *))
 {
@@ -441,14 +442,78 @@ loopingroups(*this,ss,sh->number-1,&pp,I,callback);
 }
 
 
+template<typename T>
+void constloopingroups(const Tensor<T> &t, int ngroup, int igroup, const T **p, SUPERINDEX &I, void (*callback)(const SUPERINDEX &, const T *))
+{
+LA_index istart,iend;
+const indexgroup *sh = &t.shape[ngroup];
+switch(sh->symmetry)
+	{
+	case 0:
+		istart= sh->offset;
+		iend=   sh->offset+sh->range-1;
+		break;
+	case 1:
+		istart= sh->offset;
+		if(igroup==sh->number-1) iend=   sh->offset+sh->range-1;
+		else iend = I[ngroup][igroup+1];
+		break;
+	case -1:
+		istart= sh->offset + igroup;
+		if(igroup==sh->number-1) iend=   sh->offset+sh->range-1;
+                else iend = I[ngroup][igroup+1]-1;
+		break;
+	}
+
+for(LA_index i = istart; i<=iend; ++i)
+	{
+	I[ngroup][igroup]=i;
+	if(ngroup==0 && igroup==0) 
+		{
+		int sign;
+		//std::cout <<"TEST  "<<t.index(&sign,I)<<" ";
+		(*callback)(I,(*p)++);
+		}
+	else 
+		{
+		int newigroup= igroup-1;
+		int newngroup=ngroup;
+		if(newigroup<0)
+			{
+			--newngroup;
+			const indexgroup *sh2 = &(* const_cast<const NRVec<indexgroup> *>(&t.shape))[newngroup];
+			newigroup=sh2->number-1;
+			}
+		constloopingroups(t,newngroup,newigroup,p,I,callback);
+		}
+	}
+}
+
+
+template<typename T>
+void Tensor<T>::constloopover(void (*callback)(const SUPERINDEX &, const T *)) const
+{
+SUPERINDEX I(shape.size());
+for(int i=0; i<I.size(); ++i)
+	{
+	const indexgroup *sh = &shape[i];
+	I[i].resize(sh->number); 
+	I[i] = sh->offset;
+	}
+const T *pp=&data[0];
+int ss=shape.size()-1;
+const indexgroup *sh = &shape[ss];
+constloopingroups(*this,ss,sh->number-1,&pp,I,callback);
+}
+
+
 static std::ostream *sout;
 template<typename T>
-static void outputcallback(const SUPERINDEX &I, T *v)
+static void outputcallback(const SUPERINDEX &I, const T *v)
 {
 //print indices flat
 for(int i=0; i<I.size(); ++i)
 	for(int j=0; j<I[i].size(); ++j) *sout << I[i][j]<<" ";
-//*sout<<" "<< " "<<(void *)v<<" "<< *v<<std::endl;
 *sout<<" "<< *v<<std::endl;
 }
 
@@ -480,7 +545,7 @@ std::ostream & operator<<(std::ostream &s, const Tensor<T> &x)
 {
 s<<x.shape;
 sout= &s;
-const_cast<Tensor<T> *>(&x)->loopover(&outputcallback<T>);
+x.constloopover(&outputcallback<T>);
 return s;
 }
 
@@ -521,6 +586,28 @@ loopovergroups(*this,shape.size()-1,&pp,I,callback);
 }
 
 
+
+
+template<typename T>
+void constloopovergroups(const Tensor<T> &t, int ngroup, const T **p, GROUPINDEX &I, void (*callback)(const GROUPINDEX &, const T *))
+{
+for(LA_largeindex i = 0; i<t.groupsizes[ngroup]; ++i)
+	{
+	I[ngroup]=i;
+	if(ngroup==0) (*callback)(I,(*p)++);
+	else constloopovergroups(t,ngroup-1,p,I,callback);
+	}
+}
+
+template<typename T>
+void Tensor<T>::constgrouploopover(void (*callback)(const GROUPINDEX &, const T *)) const
+{
+GROUPINDEX I(shape.size());
+const T *pp= &data[0]; 
+constloopovergroups(*this,shape.size()-1,&pp,I,callback);
+}
+
+
 const NRPerm<int> *help_p;
 template<typename T> 
 Tensor<T> *help_t;
@@ -528,7 +615,7 @@ template<typename T>
 const Tensor<T> *help_tt;
 
 template<typename T>
-static void permutecallback(const GROUPINDEX &I, T *v)
+static void permutecallback(const GROUPINDEX &I, const T *v)
 {
 LA_largeindex target=0;
 for(int i=0; i< help_t<T>->shape.size(); ++i)
@@ -553,7 +640,7 @@ help_p = &p;
 help_t<T> = &r;
 
 //now rearrange the data
-const_cast<Tensor<T> *>(this)->grouploopover(permutecallback<T>);
+const_cast<Tensor<T> *>(this)->constgrouploopover(permutecallback<T>);
 return r;
 }
 
diff --git a/tensor.h b/tensor.h
index 83becb9..f06e6ec 100644
--- a/tensor.h
+++ b/tensor.h
@@ -49,8 +49,6 @@
 //@@@conversions to/from fourindex, optional negarive rande for beta spin handling
 //@@@ optional distinguish covariant and contravariant check in contraction
 //
-//maybe const loopover and grouploopover to avoid problems with shallowly copied tensors
-//
 //@@@?general permutation of individual indices - check the indices in sym groups remain adjacent, calculate result's shape, loopover the result and permute using unwind_callback
 //
 //
@@ -224,7 +222,9 @@ public:
 	inline void randomize(const typename LA_traits<T>::normtype &x) {data.randomize(x);};
 
 	void loopover(void (*callback)(const SUPERINDEX &, T *)); //loop over all elements
+	void constloopover(void (*callback)(const SUPERINDEX &, const T *)) const; //loop over all elements
 	void grouploopover(void (*callback)(const GROUPINDEX &, T *)); //loop over all elements disregarding the internal structure of index groups
+	void constgrouploopover(void (*callback)(const GROUPINDEX &, const T *)) const; //loop over all elements disregarding the internal structure of index groups
 
 	Tensor permute_index_groups(const NRPerm<int> &p) const; //rearrange the tensor storage permuting index groups as a whole
 	Tensor unwind_index(int group, int index) const; //separate an index from a group and expand it to full range as the least significant one (the leftmost one)