Add rudimentary int class with bit index

This needs to be changed to have the PPC bit ordering

diff --git a/src/soc/decoder/selectable_int.py b/src/soc/decoder/selectable_int.py
new file mode 100644 (file)
index 0000000..daa834a
--- /dev/null
+++ b/src/soc/decoder/selectable_int.py
@@ -0,0 +1,57 @@
+import unittest
+class SelectableInt:
+    def __init__(self, value, bits):
+        self.value = value
+        self.bits = bits
+
+    def __add__(self, b):
+        assert b.bits == self.bits
+        return SelectableInt(self.value + b.value, self.bits)
+
+    def __getitem__(self, key):
+        if isinstance(key, int):
+            assert key < self.bits
+            assert key >= 0
+
+            value = (self.value >> key) & 1
+            return SelectableInt(value, 1)
+        elif isinstance(key, slice):
+            assert key.step is None or key.step == 1
+            assert key.start < key.stop
+            assert key.start >= 0
+            assert key.stop <= self.bits
+
+            bits = key.stop - key.start
+            mask = (1 << bits) - 1
+            value = (self.value >> key.start) & mask
+            return SelectableInt(value, bits)
+    
+    def __eq__(self, other):
+        if isinstance(other, SelectableInt):
+            return other.value == self.value and other.bits == self.bits
+        if isinstance(other, int):
+            return other == self.value
+        assert False
+
+    def __repr__(self):
+        return "SelectableInt(value={:x}, bits={})".format(self.value, self.bits)
+
+
+class SelectableIntTestCase(unittest.TestCase):
+    def test_add(self):
+        a = SelectableInt(5, 8)
+        b = SelectableInt(9, 8)
+        c = a + b
+        assert c.value == a.value + b.value
+        assert c.bits == a.bits
+
+    def test_select(self):
+        a = SelectableInt(0xa5, 8)
+        assert a[0] == 1
+        assert a[0:1] == 1
+        assert a[0:4] == 5
+        assert a[4:8] == 10
+
+
+if __name__ == "__main__":
+    unittest.main()