Fix div-by-0, some javadoc

higher level parsers can return null, but their return is ignored anycase.
div-by-0 is defined to be 0, backported to ch2,3,4,5

4 files changed, 17 insertions, 16 deletions

diff --git a/chapter05/src/main/java/com/seaofnodes/simple/Parser.java b/chapter05/src/main/java/com/seaofnodes/simple/Parser.java
index 0d7114d8..92b1f0d5 100644
--- a/chapter05/src/main/java/com/seaofnodes/simple/Parser.java
+++ b/chapter05/src/main/java/com/seaofnodes/simple/Parser.java
@@ -107,7 +107,7 @@ public class Parser {
      * <pre>
      *     '{' statements '}'
      * </pre>
-     * @return a {@link Node}, never {@code null}
+     * @return a {@link Node} or {@code null}
      */
     private Node parseBlock() {
         // Enter a new scope
@@ -128,7 +128,7 @@ public class Parser {
      * <pre>
      *     returnStatement | declStatement | blockStatement | expressionStatement
      * </pre>
-     * @return a {@link Node}, never {@code null}
+     * @return a {@link Node} or {@code null}
      */
     private Node parseStatement() {
         if (matchx("return")  ) return parseReturn();
@@ -200,12 +200,12 @@ public class Parser {
 
     /**
      * Dumps out the node graph
-     * @return a {@link Node}, never {@code null}
+     * @return {@code null}
      */
     private Node showGraph() {
         require(";");
         System.out.println(new GraphVisualizer().generateDotOutput(this));
-        return ctrl();
+        return null;
     }
 
     /**
diff --git a/chapter05/src/main/java/com/seaofnodes/simple/node/DivNode.java b/chapter05/src/main/java/com/seaofnodes/simple/node/DivNode.java
index 22167a87..1f562378 100644
--- a/chapter05/src/main/java/com/seaofnodes/simple/node/DivNode.java
+++ b/chapter05/src/main/java/com/seaofnodes/simple/node/DivNode.java
@@ -23,11 +23,10 @@ public class DivNode extends Node {
     public Type compute() {
         if (in(1)._type instanceof TypeInteger i0 &&
             in(2)._type instanceof TypeInteger i1) {
-            if (i0.isConstant() && i1.isConstant()) {
-                if (i1.value() == 0)
-                    throw new IllegalArgumentException("Divide by zero");
-                return TypeInteger.constant(i0.value()/i1.value());
-            }
+            if (i0.isConstant() && i1.isConstant())
+                return i1.value() == 0
+                    ? TypeInteger.ZERO
+                    : TypeInteger.constant(i0.value()/i1.value());
             return i0.meet(i1);
         }
         return TypeBot.BOTTOM;
diff --git a/chapter05/src/main/java/com/seaofnodes/simple/type/TypeInteger.java b/chapter05/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
index f75a6788..63c46035 100644
--- a/chapter05/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
+++ b/chapter05/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
@@ -7,6 +7,7 @@ public class TypeInteger extends Type {
 
     public final static TypeInteger TOP = new TypeInteger(false, 0);
     public final static TypeInteger BOT = new TypeInteger(false, 1);
+    public final static TypeInteger ZERO= new TypeInteger(true, 0);
 
     private final boolean _is_con;
 
diff --git a/chapter05/src/test/java/com/seaofnodes/simple/Chapter05Test.java b/chapter05/src/test/java/com/seaofnodes/simple/Chapter05Test.java
index bb95dc18..ea65900f 100644
--- a/chapter05/src/test/java/com/seaofnodes/simple/Chapter05Test.java
+++ b/chapter05/src/test/java/com/seaofnodes/simple/Chapter05Test.java
@@ -69,7 +69,13 @@ return c;
         StopNode stop = parser.parse();
         assertEquals("return Phi(Region33,Phi(Region21,2,3),Phi(Region31,4,5));", stop.toString());
     }
-
+    
+    @Test
+    public void testChapter5True() {
+      StopNode stop = new Parser("return true;").parse();
+      assertEquals("return 1;",stop.toString());
+    }
+    
     @Test
     public void testChapter5HalfDef() {
         try { 
@@ -91,12 +97,6 @@ return c;
     }
     
     @Test
-    public void testChapter5True() {
-      StopNode stop = new Parser("return true;").parse();
-      assertEquals("return 1;",stop.toString());
-    }
-    
-    @Test
     public void testChapter5BadNum() {
         try { 
             new Parser("return 1-;").parse();
@@ -135,6 +135,7 @@ return c;
             assertEquals("Syntax error, expected =: (",e.getMessage());
         }
     }
+    
     @Test
     public void testChapter4Peephole() {
         Parser parser = new Parser("return 1+arg+2; #showGraph;");