improved exception handling in the cycle detector

distribution/ReleaseNotes.txt

@@ -7,7 +7,7 @@ HEAD, planned as v0.17
 - Added an "export to zip" function.
 - If an input or output is several bits wide, all pin numbers can be specified by a comma-separated list.
 - Added a chapter "First Steps" to the documentation.
-- The model analyzer now detects circles and creates an error message if a circle is detected.
+- The model analyzer now detects cycles and creates an error message if a cycle is detected.
 - Bug fixes
   - Splitter, BarrelShifter and Comparator now are working with 64 bit.
   - fixed a bug in library IC 74198

src/main/java/de/neemann/digital/analyse/CycleDetector.java

@@ -10,22 +10,25 @@ import java.util.HashMap;
 import java.util.HashSet;
 
 /**
- * Helper to check a circuit for circles
+ * Helper to check a circuit for cycles.
+ * A cycle is a situation where a gate input depends somehow on one of its outputs.
+ * If a cycle is detected an exception is thrown.
  */
-public final class CircleDetector {
+public final class CycleDetector {
 
-    private CircleDetector() {
+    private CycleDetector() {
     }
 
     /**
-     * Returns true if the circuit has circles.
+     * Checks a circuit for circles.
+     * If a circle is detected, en exception is thrown.
      *
      * @param values the input signals of the circuit
-     * @return if the circuit has circles
      * @throws BacktrackException BacktrackException
      * @throws PinException       PinException
+     * @throws CycleException    is thrown if a circle is detected
      */
-    public static boolean hasCircles(ArrayList<Signal> values) throws BacktrackException, PinException {
+    public static void checkForCycles(ArrayList<Signal> values) throws BacktrackException, PinException, CycleException {
         HashMap<NodeInterface, Node> nodes = new HashMap<>();
         HashSet<ObservableValue> visited = new HashSet<>();
 
@@ -35,12 +38,7 @@ public final class CircleDetector {
             traverse(root, s.getValue(), nodes, visited);
         }
 
-        try {
-            checkForCircles(nodes.values());
-            return false;
-        } catch (CircleException e) {
-            return true;
-        }
+        checkGraphForCycles(nodes.values());
     }
 
     private static void traverse(Node parent, ObservableValue val, HashMap<NodeInterface, Node> nodes, HashSet<ObservableValue> visited) throws PinException, BacktrackException {
@@ -83,7 +81,7 @@ public final class CircleDetector {
         }
     }
 
-    private static void checkForCircles(Collection<Node> nodes) throws CircleException {
+    private static void checkGraphForCycles(Collection<Node> nodes) throws CycleException {
         ArrayList<Node> remaining = new ArrayList<>(nodes);
 
         int layer = 1;
@@ -104,12 +102,15 @@ public final class CircleDetector {
             }
 
             if (ableToPlace.isEmpty())
-                throw new CircleException();
+                throw new CycleException();
 
             remaining.removeAll(ableToPlace);
         }
     }
 
-    private static class CircleException extends Exception {
+    final static class CycleException extends AnalyseException {
+        private CycleException() {
+            super(Lang.get("err_circuitHasCycles"));
+        }
     }
 }

src/main/java/de/neemann/digital/analyse/ModelAnalyser.java

@@ -362,8 +362,7 @@ public class ModelAnalyser {
         for (Signal s : outputs)
             getModelAnalyzerInfo().addPinNumber(s);
 
-        if (CircleDetector.hasCircles(inputs))
-            throw new AnalyseException(Lang.get("err_circuitHasCircles"));
+        CycleDetector.checkForCycles(inputs);
 
         DependencyAnalyser da = new DependencyAnalyser(this);
         long steps = da.getRequiredSteps(this);

src/main/resources/lang/lang_de.xml

@@ -804,7 +804,7 @@ Sind evtl. die Namen der Variablen nicht eindeutig?</string>
     <string name="err_tableHasToManyResultColumns">Die Tabelle hat zu viele Spalten!</string>
     <string name="err_errorExportingZip">Fehler beim Schreiben der ZIP-Datei.</string>
     <string name="err_moreThanOneFastClock">Es ist nur ein Taktelement mit hoher Frequenz erlaubt.</string>
-    <string name="err_circuitHasCircles">Die Schaltung enthält Zyklen und kann daher nicht analysiert werden.</string>
+    <string name="err_circuitHasCycles">Die Schaltung enthält Zyklen und kann daher nicht analysiert werden.</string>
 
     <string name="key_AddrBits">Adress-Bits</string><!-- ROM, RAMDualPort, RAMSinglePort, RAMSinglePortSel, EEPROM -->
     <string name="key_AddrBits_tt">Anzahl der Adress-Bits, die verwendet werden.</string>

src/main/resources/lang/lang_en.xml

@@ -800,7 +800,7 @@ The names of the variables may not be unique.</string>
     <string name="err_tableHasToManyResultColumns">The table has too many columns!</string>
     <string name="err_errorExportingZip">Error writing the zip file.</string>
     <string name="err_moreThanOneFastClock">Only one clock component with high frequency is allowed.</string>
-    <string name="err_circuitHasCircles">The circuit contains circles. It's not possible to analyze such a circuit.</string>
+    <string name="err_circuitHasCycles">The circuit contains cycles. It's not possible to analyze such a circuit.</string>
 
     <string name="key_AddrBits">Address Bits</string><!-- ROM, RAMDualPort, RAMSinglePort, RAMSinglePortSel, EEPROM -->
     <string name="key_AddrBits_tt">Number of address bits used.</string>

src/test/java/de/neemann/digital/analyse/CycleDetectorTest.java

@@ -2,10 +2,9 @@ package de.neemann.digital.analyse;
 
 import de.neemann.digital.core.Model;
 import de.neemann.digital.integration.ToBreakRunner;
-import de.neemann.digital.lang.Lang;
 import junit.framework.TestCase;
 
-public class CircleDetectorTest extends TestCase {
+public class CycleDetectorTest extends TestCase {
 
     private static final String[] nameTableSequential = {
             "D.dig",
@@ -61,10 +60,10 @@ public class CircleDetectorTest extends TestCase {
         for (String name : nameTableSequential) {
             Model model = new ToBreakRunner("../../main/dig/sequential/" + name, false).getModel();
             try {
-                TruthTable tt = new ModelAnalyser(model).analyse();
+                new ModelAnalyser(model).analyse();
                 fail();
-            } catch (AnalyseException e) {
-                assertTrue(e.getMessage().contains(Lang.get("err_circuitHasCircles")));
+            } catch (CycleDetector.CycleException e) {
+                assertTrue(true);
             }
         }
     }
@@ -72,7 +71,7 @@ public class CircleDetectorTest extends TestCase {
     public void testCirclesOk() throws Exception {
         for (String name : nameTableCombinatorial) {
             Model model = new ToBreakRunner("../../main/dig/combinatorial/" + name, false).getModel();
-            TruthTable tt = new ModelAnalyser(model).analyse();
+            new ModelAnalyser(model).analyse();
         }
     }