Add memory storage capabilities to `ProgramState`

The `SparseMemory` class represents a program's memory. While the user
can read from and write to arbitrary memory addresses, it manages its
memory in pages/chunks internally. This is a tradeoff between space
consumption (this solution might have a memory overhead) and lookup
speed of individual memory addresses.

Add two small unit tests for `SparseMemory`.

1 files changed, 33 insertions, 0 deletions

diff --git a/test/test_sparse_memory.py b/test/test_sparse_memory.py
new file mode 100644
index 0000000..87b4456
--- /dev/null
+++ b/test/test_sparse_memory.py
@@ -0,0 +1,33 @@
+import unittest
+
+from snapshot import SparseMemory, MemoryAccessError
+
+class TestSparseMemory(unittest.TestCase):
+    def test_oob_read(self):
+        mem = SparseMemory()
+        for addr in range(mem.page_size):
+            self.assertRaises(MemoryAccessError, mem.read, addr, 1)
+            self.assertRaises(MemoryAccessError, mem.read, addr, 30)
+            self.assertRaises(MemoryAccessError, mem.read, addr + 0x10, 30)
+            self.assertRaises(MemoryAccessError, mem.read, addr, mem.page_size)
+            self.assertRaises(MemoryAccessError, mem.read, addr, mem.page_size - 1)
+            self.assertRaises(MemoryAccessError, mem.read, addr, mem.page_size + 1)
+
+    def test_basic_read_write(self):
+        mem = SparseMemory()
+
+        data = b'a' * mem.page_size * 2
+        mem.write(0x300, data)
+        self.assertEqual(mem.read(0x300, len(data)), data)
+        self.assertEqual(mem.read(0x300, 1), b'a')
+        self.assertEqual(mem.read(0x400, 1), b'a')
+        self.assertEqual(mem.read(0x299 + mem.page_size * 2, 1), b'a')
+        self.assertEqual(mem.read(0x321, 12), b'aaaaaaaaaaaa')
+
+        mem.write(0x321, b'Hello World!')
+        self.assertEqual(mem.read(0x321, 12), b'Hello World!')
+
+        self.assertRaises(MemoryAccessError, mem.read, 0x300, mem.page_size * 3)
+
+if __name__ == '__main__':
+    unittest.main()