From e9863b6fa1fd779cbd7464cd1fea236b48734f87 Mon Sep 17 00:00:00 2001
From: Kartik Singhal <kartik.singhal@quantinuum.com>
Date: Wed, 11 Sep 2024 12:00:49 -0500
Subject: [PATCH] fix: Emit nested binary expressions for classical ops (#224)

* test: add test for issue 215

* docs: provide maintainer email ID
Closes: #142

* chore: update deps

* fix: generate nested multi-bit conditions for pecos support

* test: remove dependency on pecos and more granular test

* refactor: raise TypeError on passing less than min_args

* refactor: use `min_args` in the error message

Co-authored-by: Alec Edgington <54802828+cqc-alec@users.noreply.github.com>

---------

Co-authored-by: Alec Edgington <54802828+cqc-alec@users.noreply.github.com>
---
 pyproject.toml         | 11 ++++++-----
 pytket/phir/phirgen.py | 33 ++++++++++++++++++++++++---------
 requirements.txt       |  2 +-
 tests/test_phirgen.py  | 27 +++++++++++++++++++++++++--
 4 files changed, 56 insertions(+), 17 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 0280127..7647bb5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -8,8 +8,11 @@ name = "pytket-phir"
 description = "A circuit analyzer and translator from pytket to PHIR"
 readme = "README.md"
 requires-python = ">=3.10, <3.13"
-license = {file = "LICENSE"}
-authors = [{name = "Quantinuum"}]
+license = { file = "LICENSE" }
+authors = [{ name = "Quantinuum" }]
+maintainers = [
+  { name = "Kartik Singhal", email = "Kartik.Singhal@quantinuum.com" },
+]
 
 classifiers = [
   "Environment :: Console",
@@ -50,9 +53,7 @@ where = ["."]
 
 [tool.pytest.ini_options]
 addopts = "-s -vv"
-pythonpath = [
-  "."
-]
+pythonpath = ["."]
 log_cli = true
 log_cli_level = "INFO"
 log_level = "DEBUG"
diff --git a/pytket/phir/phirgen.py b/pytket/phir/phirgen.py
index 5cfb4e0..0db08b3 100644
--- a/pytket/phir/phirgen.py
+++ b/pytket/phir/phirgen.py
@@ -11,6 +11,7 @@
 import json
 import logging
 import sys
+from collections import deque
 from copy import deepcopy
 from importlib.metadata import version
 from typing import TYPE_CHECKING, Any, TypeAlias
@@ -356,15 +357,29 @@ def convert_classicalevalop(op: tk.ClassicalEvalOp, cmd: tk.Command) -> JsonDict
 
 def multi_bit_condition(args: "list[UnitID]", value: int) -> JsonDict:
     """Construct bitwise condition."""
-    return {
-        "cop": "&",
-        "args": [
-            {"cop": "==", "args": [arg_to_bit(arg), bval]}
-            for (arg, bval) in zip(
-                args[::-1], map(int, f"{value:0{len(args)}b}"), strict=True
-            )
-        ],
-    }
+    min_args = 2
+    if len(args) < min_args:
+        msg = f"multi_bit_condition requires at least {min_args} arguments"
+        raise TypeError(msg)
+
+    def nested_cop(cop: str, args: "deque[UnitID]", val_bits: deque[int]) -> JsonDict:
+        if len(args) == min_args:
+            return {
+                "cop": cop,
+                "args": [
+                    {"cop": "==", "args": [arg_to_bit(args.popleft()), val_bits.pop()]},
+                    {"cop": "==", "args": [arg_to_bit(args.popleft()), val_bits.pop()]},
+                ],
+            }
+        return {
+            "cop": cop,
+            "args": [
+                {"cop": "==", "args": [arg_to_bit(args.popleft()), val_bits.pop()]},
+                nested_cop(cop, args, val_bits),
+            ],
+        }
+
+    return nested_cop("&", deque(args), deque(map(int, f"{value:0{len(args)}b}")))
 
 
 def convert_subcmd(op: tk.Op, cmd: tk.Command) -> JsonDict | None:  # noqa: PLR0912
diff --git a/requirements.txt b/requirements.txt
index 0649295..2e682ab 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,7 +4,7 @@ networkx<3
 phir==0.3.3
 pre-commit==3.8.0
 pydata_sphinx_theme==0.15.4
-pytest==8.3.2
+pytest==8.3.3
 pytket==1.32.0
 ruff==0.6.4
 setuptools_scm==8.1.0
diff --git a/tests/test_phirgen.py b/tests/test_phirgen.py
index bbaed38..d4a28b5 100644
--- a/tests/test_phirgen.py
+++ b/tests/test_phirgen.py
@@ -94,8 +94,8 @@ def test_pytket_classical_only() -> None:
         "condition": {
             "cop": "&",
             "args": [
-                {"cop": "==", "args": [["b", 2], 1]},
                 {"cop": "==", "args": [["b", 1], 0]},
+                {"cop": "==", "args": [["b", 2], 1]},
             ],
         },
         "true_branch": [
@@ -177,8 +177,8 @@ def test_conditional_barrier() -> None:
         "condition": {
             "cop": "&",
             "args": [
-                {"cop": "==", "args": [["m", 1], 0]},
                 {"cop": "==", "args": [["m", 0], 0]},
+                {"cop": "==", "args": [["m", 1], 0]},
             ],
         },
         "true_branch": [{"meta": "barrier", "args": [["q", 0], ["q", 1]]}],
@@ -463,3 +463,26 @@ def test_nullary_ops() -> None:
         "cop": "==",
         "args": [["tk_SCRATCH_BIT", 1], 1],  # evals to False
     }
+
+
+def test_condition_multiple_bits() -> None:
+    """From https://github.com/CQCL/pytket-phir/issues/215 ."""
+    n_bits = 3
+    c = Circuit(1, n_bits)
+    c.Rz(0.5, 0, condition_bits=list(range(n_bits)), condition_value=6)
+    phir = json.loads(pytket_to_phir(c))
+
+    assert phir["ops"][2] == {"//": "IF ([c[0], c[1], c[2]] == 6) THEN Rz(0.5) q[0];"}
+    assert phir["ops"][3]["condition"] == {
+        "cop": "&",
+        "args": [
+            {"cop": "==", "args": [["c", 0], 0]},
+            {
+                "cop": "&",
+                "args": [
+                    {"cop": "==", "args": [["c", 1], 1]},
+                    {"cop": "==", "args": [["c", 2], 1]},
+                ],
+            },
+        ],
+    }