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comparison mercurial/revlogutils/constants.py @ 47393:7a0ec25d5836

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revlog: move entry documentation alongside new related constants Accessing individual index-entry element is usually done using integer directly. This is presumably for "performance reasons". However as the index entry gain more and more element it seems useful to get the option to use symbolic constant to access item, for both clarify and versatility. We will probably keep using integer for performance critical path, but less critical code may start using them now that they are declared. Differential Revision: https://phab.mercurial-scm.org/D10791
author Pierre-Yves David <pierre-yves.david@octobus.net>
date Sat, 22 May 2021 00:06:22 +0200
parents 298d4400ea68
children a669404f0f4a
comparison
equal deleted inserted replaced
47392:8089d0fa8400 47393:7a0ec25d5836
24 KIND_CHANGELOG, 24 KIND_CHANGELOG,
25 KIND_MANIFESTLOG, 25 KIND_MANIFESTLOG,
26 KIND_FILELOG, 26 KIND_FILELOG,
27 KIND_OTHER, 27 KIND_OTHER,
28 } 28 }
29
30 ### Index entry key
31 #
32 #
33 # Internal details
34 # ----------------
35 #
36 # A large part of the revlog logic deals with revisions' "index entries", tuple
37 # objects that contains the same "items" whatever the revlog version.
38 # Different versions will have different ways of storing these items (sometimes
39 # not having them at all), but the tuple will always be the same. New fields
40 # are usually added at the end to avoid breaking existing code that relies
41 # on the existing order. The field are defined as follows:
42
43 # [0] offset:
44 # The byte index of the start of revision data chunk.
45 # That value is shifted up by 16 bits. use "offset = field >> 16" to
46 # retrieve it.
47 #
48 # flags:
49 # A flag field that carries special information or changes the behavior
50 # of the revision. (see `REVIDX_*` constants for details)
51 # The flag field only occupies the first 16 bits of this field,
52 # use "flags = field & 0xFFFF" to retrieve the value.
53 ENTRY_DATA_OFFSET = 0
54
55 # [1] compressed length:
56 # The size, in bytes, of the chunk on disk
57 ENTRY_DATA_COMPRESSED_LENGTH = 1
58
59 # [2] uncompressed length:
60 # The size, in bytes, of the full revision once reconstructed.
61 ENTRY_DATA_UNCOMPRESSED_LENGTH = 2
62
63 # [3] base rev:
64 # Either the base of the revision delta chain (without general
65 # delta), or the base of the delta (stored in the data chunk)
66 # with general delta.
67 ENTRY_DELTA_BASE = 3
68
69 # [4] link rev:
70 # Changelog revision number of the changeset introducing this
71 # revision.
72 ENTRY_LINK_REV = 4
73
74 # [5] parent 1 rev:
75 # Revision number of the first parent
76 ENTRY_PARENT_1 = 5
77
78 # [6] parent 2 rev:
79 # Revision number of the second parent
80 ENTRY_PARENT_2 = 6
81
82 # [7] node id:
83 # The node id of the current revision
84 ENTRY_NODE_ID = 7
85
86 # [8] sidedata offset:
87 # The byte index of the start of the revision's side-data chunk.
88 ENTRY_SIDEDATA_OFFSET = 8
89
90 # [9] sidedata chunk length:
91 # The size, in bytes, of the revision's side-data chunk.
92 ENTRY_SIDEDATA_COMPRESSED_LENGTH = 9
93
94 # [10] data compression mode:
95 # two bits that detail the way the data chunk is compressed on disk.
96 # (see "COMP_MODE_*" constants for details). For revlog version 0 and
97 # 1 this will always be COMP_MODE_INLINE.
98 ENTRY_DATA_COMPRESSION_MODE = 10
99
100 # [11] side-data compression mode:
101 # two bits that detail the way the sidedata chunk is compressed on disk.
102 # (see "COMP_MODE_*" constants for details)
103 ENTRY_SIDEDATA_COMPRESSION_MODE = 11
29 104
30 ### main revlog header 105 ### main revlog header
31 106
32 # We cannot rely on Struct.format is inconsistent for python <=3.6 versus above 107 # We cannot rely on Struct.format is inconsistent for python <=3.6 versus above
33 INDEX_HEADER_FMT = b">I" 108 INDEX_HEADER_FMT = b">I"