Initial (random) placer capability

This commit also includes changes to jsonparse to allow it to
1) recognize ports with no connection, and set their net pointers to NULL
2) recognize designs with a ports node rather than a ports_direction

The rule checker has also been modified to accommodate possible NULL netlists

The ice40 chip now also has iterator operations ++bi and bi++.

1 files changed, 12 insertions, 1 deletions

diff --git a/ice40/chip.h b/ice40/chip.h
index 695eea48..dd00c7c8 100644
--- a/ice40/chip.h
+++ b/ice40/chip.h
@@ -276,12 +276,23 @@ struct BelIterator
 {
     int cursor;
 
-    void operator++() { cursor++; }
+    BelIterator operator++() { cursor++; return *this; }
+    BelIterator operator++(int) {
+		BelIterator	prior(*this);
+		cursor++;
+		return prior;
+	}
+
     bool operator!=(const BelIterator &other) const
     {
         return cursor != other.cursor;
     }
 
+    bool operator==(const BelIterator &other) const
+    {
+        return cursor == other.cursor;
+    }
+
     BelId operator*() const
     {
         BelId ret;