From 8e65614d3134d980d7e57951d2f524519d30956f Mon Sep 17 00:00:00 2001
From: rlar <rlar>
Date: Sun, 8 Feb 2015 21:57:07 +0100
Subject: [PATCH] spfactor.c, cktnames.c, don't crash when simulating "nothing"

reported by Siddhant Saraf in
> [ngspice:discussion] "out of memory" error : simulating a 2bit AND gate"

This comes in two flavours,
   1) an empty circuit
   2) a xspice circuit with exclusively xspice event nodes
---
 src/maths/sparse/spfactor.c       | 11 +++++++++++
 src/spicelib/analysis/cktnames.c  |  2 +-
 tests/regression/misc/Makefile.am |  2 +-
 tests/regression/misc/empty-1.cir | 18 ++++++++++++++++++
 tests/regression/misc/empty-1.out | 26 ++++++++++++++++++++++++++
 5 files changed, 57 insertions(+), 2 deletions(-)
 create mode 100644 tests/regression/misc/empty-1.cir
 create mode 100644 tests/regression/misc/empty-1.out

diff --git a/src/maths/sparse/spfactor.c b/src/maths/sparse/spfactor.c
index bd72a9788..dcfad94ac 100644
--- a/src/maths/sparse/spfactor.c
+++ b/src/maths/sparse/spfactor.c
@@ -340,6 +340,11 @@ spFactor(MatrixPtr Matrix)
 
     Size = Matrix->Size;
 
+    if (Size == 0) {
+        Matrix->Factored = YES;
+        return (Matrix->Error = spOKAY);
+    }
+
     if (Matrix->Diag[1]->Real == 0.0) return ZeroPivot( Matrix, 1 );
     Matrix->Diag[1]->Real = 1.0 / Matrix->Diag[1]->Real;
 
@@ -443,6 +448,12 @@ FactorComplexMatrix( MatrixPtr Matrix )
     assert(Matrix->Complex);
 
     Size = Matrix->Size;
+
+    if (Size == 0) {
+        Matrix->Factored = YES;
+        return (Matrix->Error = spOKAY);
+    }
+
     pElement = Matrix->Diag[1];
     if (ELEMENT_MAG(pElement) == 0.0) return ZeroPivot( Matrix, 1 );
     /* Cmplx expr: *pPivot = 1.0 / *pPivot. */
diff --git a/src/spicelib/analysis/cktnames.c b/src/spicelib/analysis/cktnames.c
index 9fc145310..d8718ffac 100644
--- a/src/spicelib/analysis/cktnames.c
+++ b/src/spicelib/analysis/cktnames.c
@@ -22,7 +22,7 @@ CKTnames(CKTcircuit *ckt, int *numNames, IFuid **nameList)
     int i;
     *numNames = ckt->CKTmaxEqNum-1;
     *nameList = TMALLOC(IFuid, *numNames);
-    if ((*nameList) == NULL) return(E_NOMEM);
+    if (*numNames && (*nameList) == NULL) return(E_NOMEM);
     i=0;
     for (here = ckt->CKTnodes->next; here; here = here->next)  {
         (*nameList) [i++] = here->name;
diff --git a/tests/regression/misc/Makefile.am b/tests/regression/misc/Makefile.am
index 9f639b9e1..b12dab9f6 100644
--- a/tests/regression/misc/Makefile.am
+++ b/tests/regression/misc/Makefile.am
@@ -1,7 +1,7 @@
 ## Process this file with automake to produce Makefile.in
 
 
-TESTS = bugs-1.cir dollar-1.cir
+TESTS = bugs-1.cir dollar-1.cir empty-1.cir
 
 TESTS_ENVIRONMENT = ngspice_vpath=$(srcdir) $(SHELL) $(top_srcdir)/tests/bin/check.sh $(top_builddir)/src/ngspice
 
diff --git a/tests/regression/misc/empty-1.cir b/tests/regression/misc/empty-1.cir
new file mode 100644
index 000000000..9236f777c
--- /dev/null
+++ b/tests/regression/misc/empty-1.cir
@@ -0,0 +1,18 @@
+check that we can survive emptiness
+
+* (exec-spice "ngspice -b %s")
+
+* Nothingness, No circuit elements at all.
+*   We have only the implicit node "0"
+* Checks whether we can live with a
+*   zero times zero circuit matrix
+
+.control
+op
+tran 0.1m 1m
+ac lin 3 1kHz 2kHz
+echo "TEST: done"
+quit 0
+.endc
+
+.end
diff --git a/tests/regression/misc/empty-1.out b/tests/regression/misc/empty-1.out
new file mode 100644
index 000000000..b0d09f5b2
--- /dev/null
+++ b/tests/regression/misc/empty-1.out
@@ -0,0 +1,26 @@
+
+Circuit: check that we can survive emptiness
+
+Doing analysis at TEMP = 27.000000 and TNOM = 27.000000
+
+
+
+No. of Data Rows : 1
+Doing analysis at TEMP = 27.000000 and TNOM = 27.000000
+
+
+Initial Transient Solution
+--------------------------
+
+Node                                   Voltage
+----                                   -------
+
+
+
+No. of Data Rows : 59
+Doing analysis at TEMP = 27.000000 and TNOM = 27.000000
+
+
+
+No. of Data Rows : 3
+TEST: done