[PATCH v3 10/19] rv/rvgen: use class constant for init marker

[Wander Lairson Costa <wander@redhat.com>]

Replace hardcoded string literal and magic number with a class
constant for the initial state marker in DOT file parsing. The
previous implementation used the magic string "__init_" directly
in the code along with a hardcoded length of 7 for substring
extraction, which made the code less maintainable and harder to
understand.

This change introduces a class constant init_marker to serve as
a single source of truth for the initial state prefix. The code
now uses startswith() for clearer intent and calculates the
substring position dynamically using len(), eliminating the magic
number. If the marker value needs to change in the future, only
the constant definition requires updating rather than multiple
locations in the code.

The refactoring improves code readability and maintainability
while preserving the exact same runtime behavior.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
Reviewed-by: Nam Cao <namcao@linutronix.de>
---
 tools/verification/rvgen/rvgen/automata.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/verification/rvgen/rvgen/automata.py b/tools/verification/rvgen/rvgen/automata.py
index e4c0335cd0fba..cdec78a4bbbae 100644
--- a/tools/verification/rvgen/rvgen/automata.py
+++ b/tools/verification/rvgen/rvgen/automata.py
@@ -42,6 +42,7 @@ class Automata:
     """
 
     invalid_state_str = "INVALID_STATE"
+    init_marker = "__init_"
     # val can be numerical, uppercase (constant or macro), lowercase (parameter or function)
     # only numerical values should have units
     constraint_rule = re.compile(r"""
@@ -136,8 +137,8 @@ class Automata:
 
             #  "enabled_fired"}; -> enabled_fired
             state = raw_state.replace('"', '').replace('};', '').replace(',', '_')
-            if state[0:7] == "__init_":
-                initial_state = state[7:]
+            if state.startswith(self.init_marker):
+                initial_state = state[len(self.init_marker):]
             else:
                 states.append(state)
                 if "doublecircle" in self.__dot_lines[cursor]:
-- 
2.53.0