From 07acc6c794da71c4c62932b4dc262d9c712f4b98 Mon Sep 17 00:00:00 2001
From: Takahiro Ueda <t.ueda.od@juntendo.ac.jp>
Date: Tue, 27 Oct 2026 15:27:42 +0900
Subject: [PATCH] fix: prevent a possible segfault at EndModel

Fix a typo in the code that shifts entries in the coupling constant list
in CoEndModel(), which led to a segfault.

Close #925.
---
 check/fixes.frm | 77 +++++++++++++++++++++++++++++++++++++++++++++++++
 sources/model.c |  2 +-
 2 files changed, 78 insertions(+), 1 deletion(-)

diff --git a/check/fixes.frm b/check/fixes.frm
index 94c7198cf..96783c8b1 100644
--- a/check/fixes.frm
+++ b/check/fixes.frm
@@ -5245,6 +5245,83 @@ Print;
 assert succeeded?
 assert result("test") =~ expr("4+4*x")
 *--#] Issue882_6 :
+*--#[ Issue925_1 :
+* Insert an item into the list of coupling constants.
+S g2,g1;  * order-dependent segfault
+Auto V p,q;
+Model mod;
+  Particle phi1 +1;
+  Particle phi2 +1;
+  Vertex phi1 phi1 phi1 : g1;
+  Vertex phi2 phi2 phi2 : g2;
+EndModel;
+L F1 = diagrams_(mod,{phi1,phi1},{},{q1,q2},{p1,p2},1,`NoSnail_');
+L F2 = diagrams_(mod,{phi2,phi2},{},{q1,q2},{p1,p2},1,`NoSnail_');
+P +ss;
+.end
+assert succeeded?
+assert result("F1") =~ expr("
+       +
+         1/2
+         *topo_(1)
+         *node_(1,1,phi1(-q1))
+         *node_(2,1,phi1(-q2))
+         *node_(3,g1,phi1(q1),phi1(-p1),phi1(-p2))
+         *node_(4,g1,phi1(q2),phi1(p1),phi1(p2))
+")
+assert result("F2") =~ expr("
+       +
+         1/2
+         *topo_(1)
+         *node_(1,1,phi2(-q1))
+         *node_(2,1,phi2(-q2))
+         *node_(3,g2,phi2(q1),phi2(-p1),phi2(-p2))
+         *node_(4,g2,phi2(q2),phi2(p1),phi2(p2))
+")
+*--#] Issue925_1 : 
+*--#[ Issue925_2 :
+* Extend the list of coupling constants.
+#define N "15"  * N >= 12
+Auto V p,q;
+Model mod;
+  #do i=1,`N'
+    Particle phi`i' +1;
+  #enddo
+  #do i=1,`N'
+  Vertex phi`i' phi`i' phi`i' : g`i';
+  #enddo
+EndModel;
+L n = `N';
+L F1 = diagrams_(mod,{phi1,phi1},{},{q1,q2},{p1,p2},1,`NoSnail_');
+L F`N' = diagrams_(mod,{phi`N',phi`N'},{},{q1,q2},{p1,p2},1,`NoSnail_');
+P +ss;
+.end
+assert succeeded?
+assert result("F1") =~ expr("
+       +
+         1/2
+         *topo_(1)
+         *node_(1,1,phi1(-q1))
+         *node_(2,1,phi1(-q2))
+         *node_(3,g1,phi1(q1),phi1(-p1),phi1(-p2))
+         *node_(4,g1,phi1(q2),phi1(p1),phi1(p2))
+")
+n = result("n").to_i
+assert result("F#{n}") =~ expr("
+       +
+         1/2
+         *topo_(1)
+         *node_(1,1,phi#{n}(-q1))
+         *node_(2,1,phi#{n}(-q2))
+         *node_(3,g#{n},phi#{n}(q1),phi#{n}(-p1),phi#{n}(-p2))
+         *node_(4,g#{n},phi#{n}(q2),phi#{n}(p1),phi#{n}(p2))
+")
+*--#] Issue925_2 : 
+*--#[ Issue925_e1 :
+EndModel;
+.end
+assert compile_error?("EndModel statement without matching Model statement")
+*--#] Issue925_e1 : 
 *--#[ PullReq535 :
 * This test requires more than the specified 50K workspace.
 #:maxtermsize 200
diff --git a/sources/model.c b/sources/model.c
index d64e64de2..6a3fc677a 100644
--- a/sources/model.c
+++ b/sources/model.c
@@ -449,7 +449,7 @@ int CoEndModel(UBYTE *s)
 			for ( k = 0; k < m->ncouplings; k++ ) {
 				if ( sym == m->couplings[k] ) break;
 				if ( sym < m->couplings[k] ) {
-					for ( kk = m->ncouplings; kk > k; k-- )
+					for ( kk = m->ncouplings; kk > k; kk-- )
 						m->couplings[kk] = m->couplings[kk-1];
 					m->couplings[k] = sym;
 					m->ncouplings++;