back.pysim: handle out of bounds ArrayProxy indexes.

diff --git a/nmigen/back/pysim.py b/nmigen/back/pysim.py
index bd90d7a5af83548c361232138587f83a36e51822..87fef0c9f525dd014b3bab008e75a761f4e1f232 100644 (file)
--- a/nmigen/back/pysim.py
+++ b/nmigen/back/pysim.py
@@ -193,7 +193,12 @@ class _RHSValueCompiler(AbstractValueTransformer):
         shape  = value.shape()
         elems  = list(map(self, value.elems))
         index  = self(value.index)
-        return lambda state: normalize(elems[index(state)](state), shape)
+        def eval(state):
+            index_value = index(state)
+            if index_value >= len(elems):
+                index_value = len(elems) - 1
+            return normalize(elems[index_value](state), shape)
+        return eval
 
 
 class _LHSValueCompiler(AbstractValueTransformer):
@@ -263,7 +268,10 @@ class _LHSValueCompiler(AbstractValueTransformer):
         elems = list(map(self, value.elems))
         index = self.rhs_compiler(value.index)
         def eval(state, rhs):
-            elems[index(state)](state, rhs)
+            index_value = index(state)
+            if index_value >= len(elems):
+                index_value = len(elems) - 1
+            elems[index_value](state, rhs)
         return eval
 
 

diff --git a/nmigen/test/test_sim.py b/nmigen/test/test_sim.py
index 963652a5d24658b1c2365f227b3fe05c1000fdb6..070fcdb0115cd802ac085789f446d28ce485c4de 100644 (file)
--- a/nmigen/test/test_sim.py
+++ b/nmigen/test/test_sim.py
@@ -184,6 +184,12 @@ class SimulatorUnitTestCase(FHDLTestCase):
         self.assertStatement(stmt, [C(1)], C(4))
         self.assertStatement(stmt, [C(2)], C(10))
 
+    def test_array_oob(self):
+        array = Array([1, 4, 10])
+        stmt = lambda y, a: y.eq(array[a])
+        self.assertStatement(stmt, [C(3)], C(10))
+        self.assertStatement(stmt, [C(4)], C(10))
+
     def test_array_lhs(self):
         l = Signal(3, reset=1)
         m = Signal(3, reset=4)
@@ -194,6 +200,15 @@ class SimulatorUnitTestCase(FHDLTestCase):
         self.assertStatement(stmt, [C(1), C(0b010)], C(0b111010001))
         self.assertStatement(stmt, [C(2), C(0b100)], C(0b100100001))
 
+    def test_array_lhs_oob(self):
+        l = Signal(3)
+        m = Signal(3)
+        n = Signal(3)
+        array = Array([l, m, n])
+        stmt = lambda y, a, b: [array[a].eq(b), y.eq(Cat(*array))]
+        self.assertStatement(stmt, [C(3), C(0b001)], C(0b001000000))
+        self.assertStatement(stmt, [C(4), C(0b010)], C(0b010000000))
+
     def test_array_index(self):
         array = Array(Array(x * y for y in range(10)) for x in range(10))
         stmt = lambda y, a, b: y.eq(array[a][b])