Fixes #321 for arithmetic operators

ASTree.cpp

@@ -2504,8 +2504,18 @@ static int cmp_prec(PycRef<ASTNode> parent, PycRef<ASTNode> child)
         return 1;   // Always parenthesize not(x)
     if (child.type() == ASTNode::NODE_BINARY) {
         PycRef<ASTBinary> binChild = child.cast<ASTBinary>();
-        if (parent.type() == ASTNode::NODE_BINARY)
-            return binChild->op() - parent.cast<ASTBinary>()->op();
+        if (parent.type() == ASTNode::NODE_BINARY) {
+            PycRef<ASTBinary> binParent = parent.cast<ASTBinary>();
+            if (binParent->right() == child) {
+                if (binParent->op() == ASTBinary::BIN_SUBTRACT &&
+                    binChild->op() == ASTBinary::BIN_ADD)
+                    return 1;
+                else if (binParent->op() == ASTBinary::BIN_DIVIDE &&
+                         binChild->op() == ASTBinary::BIN_MULTIPLY)
+                    return 1;
+            }
+            return binChild->op() - binParent->op();
+        }
         else if (parent.type() == ASTNode::NODE_COMPARE)
             return (binChild->op() == ASTBinary::BIN_LOG_AND ||
                     binChild->op() == ASTBinary::BIN_LOG_OR) ? 1 : -1;

tests/input/op_precedence.py

@@ -0,0 +1,8 @@
+def foo(a, b, c):
+    return c - (a + b) 
+
+def bar(a, b, c, d):
+    return a / ((b ** c) * d)
+
+def baz(a, b, c, d):
+    return a - ((b ^ c) + d)

tests/tokenized/op_precedence.txt

@@ -0,0 +1,11 @@
+def foo ( a , b , c ) : <EOL>
+<INDENT>
+return c - ( a + b ) <EOL>
+<OUTDENT>
+def bar ( a , b , c , d ) : <EOL>
+<INDENT>
+return a / ( b ** c * d ) <EOL>
+<OUTDENT>
+def baz ( a , b , c , d ) : <EOL>
+<INDENT>
+return a - ( ( b ^ c ) + d ) <EOL>