From 4f8293dbf09fa202b2d0ca1c3d62667026b74b75 Mon Sep 17 00:00:00 2001
From: Jiri Pittner <jiri@pittnerovi.com>
Date: Thu, 30 Oct 2025 15:25:06 +0100
Subject: [PATCH] tensor lhs() signedpointer debug diagnostics

---
 t.cc     | 26 ++++++++++++++++++++++++--
 tensor.h | 15 +++++++++++----
 2 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/t.cc b/t.cc
index 789de85..4af391f 100644
--- a/t.cc
+++ b/t.cc
@@ -3853,7 +3853,7 @@ for(int l=1; l<=n; ++l)
 }
 
 
-if(1)
+if(0)
 {
 int n;
 cin>>n;
@@ -3879,7 +3879,29 @@ for(int l=1; l<=n; ++l)
 
 }
 
-
+if(1)
+{
+//tensor lhs operator() and signed pointer
+int n;
+cin >>n;
+INDEXGROUP shape;
+        {
+        shape.number=3;
+        shape.symmetry= -1;
+        shape.range=n;
+        shape.offset=0;
+        }
+Tensor<double> t(shape);
+t.clear();
+for(int i=0; i<n; ++i)
+for(int j=0; j<n; ++j)
+for(int k=0; k<n; ++k)
+	{
+	//cout <<t(i,j,k)<<endl;
+	if(i!=j && i!=k &&j!=k) t.lhs(i,j,k) = 10.*random()/RAND_MAX;
+	}
+cout <<t;
+}
 
 
 
diff --git a/tensor.h b/tensor.h
index ce1590a..cc64ec6 100644
--- a/tensor.h
+++ b/tensor.h
@@ -46,8 +46,7 @@
 //@@@ will need to store vector of INDEX to the original tensor for the result's flatindex
 //@@@ will not be particularly efficient
 //
-//@@@conversions to/from fourindex, optional negative range for beta spin handling in some cases
-//@@@check operator() for all fourindex-tensor conversions
+//maybe optional negative range for beta spin handling in some cases of fourindex-tensor conversions
 //
 //@@@?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
 //
@@ -67,8 +66,16 @@ T *ptr;
 int sgn;
 public:
 	Signedpointer(T *p, int s) : ptr(p),sgn(s) {};
-	//dereferencing *ptr  should intentionally segfault for sgn==0
-	T& operator=(const T rhs) {if(sgn>0) *ptr=rhs; else *ptr = -rhs; return *ptr;}
+	//dereferencing *ptr  should be ignored for sgn==0
+	const T operator=(const T rhs) 
+			{
+			if(sgn>0) *ptr = rhs; 
+			if(sgn<0) *ptr = -rhs; 
+#ifdef DEBUG
+			if(sgn==0) laerror("dereferencing lhs Signedpointer to nonexistent tensor element");
+#endif
+			return rhs;
+			}
 	T& operator*=(const T rhs) {*ptr *= rhs; return *ptr;}
 	T& operator/=(const T rhs) {*ptr /= rhs; return *ptr;}
 	T& operator+=(const T rhs) {if(sgn>0) *ptr += rhs; else *ptr -= rhs; return *ptr;}