fix: fix signed integer casting (#261)

src/braket/default_simulator/openqasm/_helpers/casting.py

@@ -86,12 +86,14 @@ def _(into: IntType, variable: LiteralType) -> IntegerLiteral:
     if isinstance(variable, ArrayLiteral):
         value = int("".join("01"[x.value] for x in variable.values[1:]), base=2)
         if variable.values[0].value:
-            value *= -1
+            value -= 2 ** (len(variable.values) - 1)
     else:
         value = variable.value
         if into.size is not None:
-            limit = 2 ** (into.size.value - 1)
-            value = int(np.sign(value) * (np.abs(int(value)) % limit))
+            limit = 2**into.size.value
+            value = int(value) % limit
+            if (value) >= limit / 2:
+                value -= limit
             if value != variable.value:
                 warnings.warn(
                     f"Integer overflow for value {variable.value} and size {into.size.value}."

test/unit_tests/braket/default_simulator/openqasm/test_interpreter.py

@@ -113,6 +113,8 @@ def test_int_declaration():
     int[8] uninitialized;
     int[8] pos = 10;
     int[5] neg = -4;
+    int[8] int_min = -128;
+    int[8] int_max = 127;
     int[3] pos_overflow = 5;
     int[3] neg_overflow = -6;
     int no_size = 1e9;
@@ -133,8 +135,10 @@ def test_int_declaration():
     assert context.get_value("uninitialized") is None
     assert context.get_value("pos") == IntegerLiteral(10)
     assert context.get_value("neg") == IntegerLiteral(-4)
-    assert context.get_value("pos_overflow") == IntegerLiteral(1)
-    assert context.get_value("neg_overflow") == IntegerLiteral(-2)
+    assert context.get_value("int_min") == IntegerLiteral(-128)
+    assert context.get_value("int_max") == IntegerLiteral(127)
+    assert context.get_value("pos_overflow") == IntegerLiteral(-3)
+    assert context.get_value("neg_overflow") == IntegerLiteral(2)
     assert context.get_value("no_size") == IntegerLiteral(1_000_000_000)
 
     warnings = {(warn.category, warn.message.args[0]) for warn in warn_info}
@@ -173,6 +177,34 @@ def test_uint_declaration():
     assert context.get_value("no_size") == IntegerLiteral(1_000_000_000)
 
 
+def test_signed_int_cast():
+    qasm = """
+    uint[8] x0 = 255;
+    int[8] x1 = x0;
+    uint[8] x2 = x1;
+
+    uint[8] y0 = 128;
+    int[8] y1 = y0;
+    uint[8] y2 = y1;
+
+    int[3] z0 = "100";
+    int[3] z1 = "111";
+    """
+
+    context = Interpreter().run(qasm)
+
+    assert context.get_value("x0") == IntegerLiteral(255)
+    assert context.get_value("x1") == IntegerLiteral(-1)
+    assert context.get_value("x2") == IntegerLiteral(255)
+
+    assert context.get_value("y0") == IntegerLiteral(128)
+    assert context.get_value("y1") == IntegerLiteral(-128)
+    assert context.get_value("y2") == IntegerLiteral(128)
+
+    assert context.get_value("z0") == IntegerLiteral(-4)
+    assert context.get_value("z1") == IntegerLiteral(-1)
+
+
 def test_float_declaration():
     qasm = """
     float[16] uninitialized;
@@ -674,7 +706,7 @@ def test_update_bits_int():
     """
     context = Interpreter().run(qasm)
     assert context.get_value("x") == IntegerLiteral(3)
-    assert context.get_value("y") == IntegerLiteral(-2)
+    assert context.get_value("y") == IntegerLiteral(-6)
     assert context.get_value("z") == IntegerLiteral(10)