From addf32f2935c756bb5cec01af905a29e6011dd42 Mon Sep 17 00:00:00 2001
From: SS <66886825+EarlMilktea@users.noreply.github.com>
Date: Thu, 19 Sep 2024 23:41:47 +0900
Subject: [PATCH] :recycle: Use bit_length

Co-authored-by: thierry-martinez <thierry.martinez@inria.fr>
---
 graphix/channels.py | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/graphix/channels.py b/graphix/channels.py
index eed024c5..83d4cde2 100644
--- a/graphix/channels.py
+++ b/graphix/channels.py
@@ -3,7 +3,6 @@
 from __future__ import annotations
 
 import copy
-import itertools
 import typing
 from typing import TYPE_CHECKING, SupportsIndex, TypeVar
 
@@ -18,12 +17,9 @@
 
 
 def _ilog2(n: int) -> int:
-    if n < 0:
-        raise ValueError("n must be non-negative.")
-    for p in itertools.count():
-        if n <= 2**p:
-            return p
-    raise RuntimeError("Unreachable.")
+    if n <= 0:
+        raise ValueError("n must be positive.")
+    return (n - 1).bit_length()
 
 
 # MEMO: Too much?