Switch to packing fields for sha512_encode

The easy solution was to render the `st_dev, st_ino, st_mtime` to a
string and encode that before hashing.

This solution is more efficient because it packs the numbers as bytes
rather than the digits. Technically POSIX.1 does not specify an upper
limit on the sizes for these fields. I think it's safe to say none of
the major operating systems will use more than 8 bytes/64 bits any time
soon.

1 files changed, 7 insertions, 5 deletions

diff --git a/ranger/core/actions.py b/ranger/core/actions.py
index 91f94f77..e76adc87 100644
--- a/ranger/core/actions.py
+++ b/ranger/core/actions.py
@@ -17,6 +17,7 @@ import tempfile
 from inspect import cleandoc
 from stat import S_IEXEC
 from hashlib import sha512
+from struct import pack
 from logging import getLogger
 
 import ranger
@@ -1049,11 +1050,12 @@ class Actions(  # pylint: disable=too-many-instance-attributes,too-many-public-m
     @staticmethod
     def sha512_encode(path):
         stat_ = stat(path)
-        sha = sha512(
-            '{dev},{inode},{mtime}'.format(
-                dev=stat_.st_dev, inode=stat_.st_ino, mtime=stat_.st_mtime
-            ).encode('utf-8', 'backslashreplace')
-        )
+        # How I arrived at the pack format string:
+        #   < -> little-endian
+        #   l -> st_dev: signed int (32/64 bits depending on platform)
+        #   L -> st_ino: unsigned int (ditto)
+        #   d -> st_mtime: double in python
+        sha = sha512(pack('<lLd', stat_.st_dev, stat_.st_ino, stat_.st_mtime))
         return '{0}.jpg'.format(sha.hexdigest())
 
     def get_preview(self, fobj, width, height):  # pylint: disable=too-many-return-statements