From c5d8ad792ead0eaa98f47a6793cb0add96b9c0c5 Mon Sep 17 00:00:00 2001
From: rlar <rlar>
Date: Mon, 15 Jan 2018 19:01:15 +0100
Subject: [PATCH] analysis/acsetp.c, ac analysis, allow frequency=0

---
 src/spicelib/analysis/acsetp.c    |  8 ++++----
 tests/regression/misc/Makefile.am |  2 +-
 tests/regression/misc/ac-zero.cir | 27 +++++++++++++++++++++++++++
 tests/regression/misc/ac-zero.out |  1 +
 4 files changed, 33 insertions(+), 5 deletions(-)
 create mode 100644 tests/regression/misc/ac-zero.cir
 create mode 100644 tests/regression/misc/ac-zero.out

diff --git a/src/spicelib/analysis/acsetp.c b/src/spicelib/analysis/acsetp.c
index d6571d7a0..7f6d79ebc 100644
--- a/src/spicelib/analysis/acsetp.c
+++ b/src/spicelib/analysis/acsetp.c
@@ -22,8 +22,8 @@ ACsetParm(CKTcircuit *ckt, JOB *anal, int which, IFvalue *value)
     switch(which) {
 
     case AC_START:
-	if (value->rValue <= 0.0) {
-	    errMsg = copy("Frequency of 0 is invalid for AC start");
+	if (value->rValue < 0.0) {
+	    errMsg = copy("Frequency of < 0 is invalid for AC start");
             job->ACstartFreq = 1.0;
 	    return(E_PARMVAL);
 	}
@@ -32,8 +32,8 @@ ACsetParm(CKTcircuit *ckt, JOB *anal, int which, IFvalue *value)
         break;
 
     case AC_STOP:
-	if (value->rValue <= 0.0) {
-	    errMsg = copy("Frequency of 0 is invalid for AC stop");
+	if (value->rValue < 0.0) {
+	    errMsg = copy("Frequency of < 0 is invalid for AC stop");
             job->ACstartFreq = 1.0;
 	    return(E_PARMVAL);
 	}
diff --git a/tests/regression/misc/Makefile.am b/tests/regression/misc/Makefile.am
index 6dd123faf..acd352b45 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 bugs-2.cir dollar-1.cir empty-1.cir resume-1.cir log-functions-1.cir alter-vec.cir test-noise-2.cir test-noise-3.cir
+TESTS = bugs-1.cir bugs-2.cir dollar-1.cir empty-1.cir resume-1.cir log-functions-1.cir alter-vec.cir test-noise-2.cir test-noise-3.cir ac-zero.cir
 
 TESTS_ENVIRONMENT = ngspice_vpath=$(srcdir) $(SHELL) $(top_srcdir)/tests/bin/check.sh $(top_builddir)/src/ngspice
 
diff --git a/tests/regression/misc/ac-zero.cir b/tests/regression/misc/ac-zero.cir
new file mode 100644
index 000000000..2ecbbf8c8
--- /dev/null
+++ b/tests/regression/misc/ac-zero.cir
@@ -0,0 +1,27 @@
+* whether .ac works for freq=0
+*
+* (exec-spice "ngspice -b %s" t)
+
+v1  1 0  dc=0 ac=1
+r1  1 2  1k
+l1  2 3  1uH
+r3  3 0  1k
+c3  3 0  1uF
+
+.control
+
+ac lin 1 0Hz 0Hz
+
+let v3_gold = 0.5
+
+let err = abs(v(3)/v3_gold - 1)
+
+if err > 1e-15
+  echo "ERROR: test failed, excessive error, err = $&err"
+  quit 1
+else
+  echo "INFO: success"
+  quit 0
+end
+
+.endc
diff --git a/tests/regression/misc/ac-zero.out b/tests/regression/misc/ac-zero.out
new file mode 100644
index 000000000..8e9036969
--- /dev/null
+++ b/tests/regression/misc/ac-zero.out
@@ -0,0 +1 @@
+INFO: success