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

@@ -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. */

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;

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
 

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

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