From 279d71b0068a26c5c5233f057beef2967194b596 Mon Sep 17 00:00:00 2001
From: Ned Batchelder <ned@nedbatchelder.com>
Date: Mon, 2 Jan 2017 11:28:39 -0500
Subject: Small improvements to the debug stuff

---
 coverage/debug.py | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/coverage/debug.py b/coverage/debug.py
index c5c9924..91ccba7 100644
--- a/coverage/debug.py
+++ b/coverage/debug.py
@@ -132,6 +132,14 @@ def dump_stack_frames(limit=None, out=None, skip=0):
     out.write("\n")
 
 
+def short_id(id64):
+    """Given a 64-bit id, make a shorter 16-bit one."""
+    id16 = 0
+    for offset in range(0, 64, 16):
+        id16 ^= id64 >> offset
+    return id16 & 0xFFFF
+
+
 class DebugOutputFile(object):                              # pragma: debugging
     """A file-like object that includes pid and cwd information."""
     def __init__(self, outfile):
@@ -171,17 +179,13 @@ class DebugOutputFile(object):                              # pragma: debugging
     def _write(self, text, stack=False):
         """The raw text-writer, so that we can use it ourselves."""
         # Thread ids are useful, but too long. Make a shorter one.
-        tid = _thread.get_ident()
-        stid = 0
-        for byte in range(4):
-            stid ^= tid >> (16 * byte)
-        stid = "{0:04x}".format(stid & 0xFFFF)
+        tid = "{0:04x}".format(short_id(_thread.get_ident()))
 
         # Aspectlib prints stack traces, but includes its own frames.  Scrub those out:
         # <<< aspectlib/__init__.py:257:function_wrapper < igor.py:143:run_tests < ...
         text = re.sub(r"(?<= )aspectlib/[^.]+\.py:\d+:\w+ < ", "", text)
 
-        self.outfile.write("{0:5d}.{1}: {2}".format(os.getpid(), stid, text))
+        self.outfile.write("{0:5d}.{1}: {2}".format(os.getpid(), tid, text))
         self.outfile.flush()
         if stack:
             dump_stack_frames(out=self.outfile, skip=1)
@@ -213,7 +217,9 @@ def enable_aspectlib_maybe():                               # pragma: debugging
     import aspectlib.debug                      # pylint: disable=import-error
 
     aspects_file = DebugOutputFile.the_one()
-    aspect_log = aspectlib.debug.log(print_to=aspects_file, attributes=['id'], stacktrace=30, use_logging=False)
+    aspect_log = aspectlib.debug.log(
+        print_to=aspects_file, attributes=['id'], stacktrace=30, use_logging=False
+    )
     public_methods = re.compile(r'^(__init__|[a-zA-Z].*)$')
     for aspect in aspects.split(':'):
         aspectlib.weave(aspect, aspect_log, methods=public_methods)
-- 
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