Fix some issues with measurements and conditional expressions

- Classical register now are initialised to 0
- Fixed bug with measurements of registers with size > 1
- Fixed issue with conditional expressions and registers with size > 1

Author: Takishima

projectq/libs/qasm/_parse_qasm_qiskit.py

@@ -15,7 +15,7 @@
 
 from projectq.ops import All, Measure, ControlledGate, SwapGate
 
-from qiskit.circuit import QuantumCircuit
+from qiskit.circuit import QuantumCircuit, ClassicalRegister, Clbit
 
 from ._qiskit_conv import gates_conv_table
 
@@ -68,7 +68,8 @@ def apply_op(eng, gate, qubits, bits, bits_map):
         eng.flush()
 
         for idx, bit in enumerate(bits):
-            bits_map[bit.register.name][idx] = bool(qubits[idx])
+            assert isinstance(bit, Clbit)
+            bits_map[bit.register.name][bit.index] = bool(qubits[idx])
     else:
         if gate.name not in gates_conv_table:
             if not gate._definition:
@@ -93,9 +94,14 @@ def apply_op(eng, gate, qubits, bits, bits_map):
                 # OpenQASM 2.0
                 cbit, value = gate.condition
 
-                # Note: apparently, it is illegal to write if (c0[0] == 1)
-                #      so we always assume that index == 0...
-                if bits_map[cbit.name][0] == value:
+                if cbit.size == 1:
+                    cbit_value = bits_map[cbit.name][0]
+                else:
+                    cbit_value = 0
+                    for bit in bits_map[cbit.name]:
+                        cbit_value = (cbit_value << 1) | bit
+
+                if cbit_value == value:
                     apply_gate(gate_projectq, qubits)
             else:
                 apply_gate(gate_projectq, qubits)
@@ -120,7 +126,7 @@ def _convert_qiskit_circuit(eng, qc):
         qureg.name: eng.allocate_qureg(qureg.size)
         for qureg in qc.qregs
     }
-    bits_map = {bit.name: [None] * bit.size for bit in qc.cregs}
+    bits_map = {bit.name: [False] * bit.size for bit in qc.cregs}
 
     # Convert all the gates to ProjectQ commands
     for gate, quregs, bits in qc.data:
@@ -131,6 +137,7 @@ def _convert_qiskit_circuit(eng, qc):
 
     return qubits_map, bits_map
 
+
 def read_qasm_str(eng, qasm_str):
     """
     Read an OpenQASM (2.0, 3.0 is experimental) string and convert it to

projectq/libs/qasm/_parse_qasm_qiskit_test.py

@@ -144,7 +144,7 @@ def test_read_qasm2_allocation(eng):
 
     engine = deepcopy(eng)
     qubits_map, bits_map = read_qasm_str(engine, qasm_str)
-    assert bits_map == {'c': [None], 'd': [None, None]}
+    assert bits_map == {'c': [False], 'd': [False, False]}
     assert len(engine.backend.received_commands) == 3
     assert all(cmd.gate == Allocate for cmd in engine.backend.received_commands)
 
@@ -321,6 +321,7 @@ def test_read_qasm2_gate_def(eng):
     assert cmd.gate == Rz(0.5)
     assert [qubit for qureg in cmd.qubits for qubit in qureg] == [b]
 
+
 def test_read_qasm2_file(eng):
     qasm_str = """
 OPENQASM 2.0;
@@ -334,12 +335,71 @@ def test_read_qasm2_file(eng):
         fd.seek(0)
         engine = deepcopy(eng)
         qubits_map, bits_map = read_qasm_file(engine, fd.name)
-        assert bits_map == {'c0': [None]}
+        assert bits_map == {'c0': [False]}
         assert len(engine.backend.received_commands) == 2
         assert engine.backend.received_commands[0].gate == Allocate
         assert engine.backend.received_commands[1].gate == Allocate
 
 
+def test_qasm_qft2(eng):
+    qasm_str = """
+OPENQASM 2.0;
+include "qelib1.inc";
+qreg a[2];
+creg b[2];
+measure a -> b;
+qreg q[3];
+creg c[3];
+// optional post-rotation for state tomography
+gate post q { }
+u3(0.3,0.2,0.1) q[0];
+h q[1];
+cx q[1],q[2];
+barrier q;
+cx q[0],q[1];
+h q[0];
+measure q[0] -> c[0];
+measure q[1] -> c[1];
+if(c==1) z q[2];
+if(c==2) x q[2];
+if(c==3) y q[2];
+if(c==4) z q[1];
+if(c==5) x q[1];
+if(c==6) y q[1];
+if(c==7) z q[0];
+if(c==8) x q[0];
+post q[2];
+measure q[2] -> c[2];
+    """
+
+    qubits_map, bits_map = read_qasm_str(eng, qasm_str)
+    assert {'q', 'a'} == set(qubits_map)
+    assert len(qubits_map['a']) == 2
+    assert len(qubits_map['q']) == 3
+    assert bits_map == {'b': [True, True], 'c': [True, True, True]}
+
+    assert len([
+        cmd for cmd in eng.backend.received_commands if cmd.gate == Allocate
+    ]) == 5
+    assert len([
+        cmd for cmd in eng.backend.received_commands
+        if isinstance(cmd.gate, U3)
+    ]) == 1
+    assert len([cmd for cmd in eng.backend.received_commands
+                if cmd.gate == X]) == 2
+    cmds = [cmd for cmd in eng.backend.received_commands if cmd.gate == Y]
+    assert len(cmds) == 1
+    assert ([qubits_map['q'][1]
+             ] == [qubit for qureg in cmds[0].qubits for qubit in qureg])
+    assert len([cmd for cmd in eng.backend.received_commands
+                if cmd.gate == Z]) == 0
+    assert len([cmd for cmd in eng.backend.received_commands
+                if cmd.gate == H]) == 2
+    cmds = [cmd for cmd in eng.backend.received_commands if cmd.gate == Barrier]
+    assert len(cmds) == 1
+    assert len([qubit for qureg in cmds[0].qubits for qubit in qureg]) == 3
+
+
 # ==============================================================================
 # OpenQASM 3.0 tests (experimental)