1 # storageutil.py - Storage functionality agnostic of backend implementation.

     2 #

     3 # Copyright 2018 Gregory Szorc <gregory.szorc@gmail.com>

     4 #

     5 # This software may be used and distributed according to the terms of the

     6 # GNU General Public License version 2 or any later version.

     7 

     8 from __future__ import absolute_import

     9 

    10 import hashlib

    11 

    12 from ..node import (

    13     nullid,

    14 )

    15 

    16 _nullhash = hashlib.sha1(nullid)

    17 

    18 def hashrevisionsha1(text, p1, p2):

    19     """Compute the SHA-1 for revision data and its parents.

    20 

    21     This hash combines both the current file contents and its history

    22     in a manner that makes it easy to distinguish nodes with the same

    23     content in the revision graph.

    24     """

    25     # As of now, if one of the parent node is null, p2 is null

    26     if p2 == nullid:

    27         # deep copy of a hash is faster than creating one

    28         s = _nullhash.copy()

    29         s.update(p1)

    30     else:

    31         # none of the parent nodes are nullid

    32         if p1 < p2:

    33             a = p1

    34             b = p2

    35         else:

    36             a = p2

    37             b = p1

    38         s = hashlib.sha1(a)

    39         s.update(b)

    40     s.update(text)

    41     return s.digest()