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| /* | |
| * xhtml11 specific | |
| * | |
| * */ | |
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| * | |
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| /* | |
| * manpage specific | |
| * | |
| * */ | |
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| @media print { | |
| body.manpage div#toc { display: none; } | |
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| <script type="text/javascript"> | |
| /*<+'])'); | |
| // Function that scans the DOM tree for header elements (the DOM2 | |
| // nodeIterator API would be a better technique but not supported by all | |
| // browsers). | |
| var iterate = function (el) { | |
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| return result; | |
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| return; | |
| } | |
| // Delete existing TOC entries in case we're reloading the TOC. | |
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| var i; | |
| for (i = 0; i < toc.childNodes.length; i++) { | |
| var entry = toc.childNodes[i]; | |
| if (entry.nodeName.toLowerCase() == 'div' | |
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| && entry.getAttribute("class").match(/^toclevel/)) | |
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| } | |
| // Rebuild TOC entries. | |
| var entries = tocEntries(document.getElementById("content"), toclevels); | |
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| if (entry.element.id == "") | |
| entry.element.id = "_toc_" + i; | |
| var a = document.createElement("a"); | |
| a.href = "#" + entry.element.id; | |
| a.appendChild(document.createTextNode(entry.text)); | |
| var div = document.createElement("div"); | |
| div.appendChild(a); | |
| div.className = "toclevel" + entry.toclevel; | |
| toc.appendChild(div); | |
| } | |
| if (entries.length == 0) | |
| toc.parentNode.removeChild(toc); | |
| }, | |
| ///////////////////////////////////////////////////////////////////// | |
| // Footnotes generator | |
| ///////////////////////////////////////////////////////////////////// | |
| /* Based on footnote generation code from: | |
| * http://www.brandspankingnew.net/archive/2005/07/format_footnote.html | |
| */ | |
| footnotes: function () { | |
| // Delete existing footnote entries in case we're reloading the footnodes. | |
| var i; | |
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| } | |
| var entriesToRemove = []; | |
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| entriesToRemove.push(entry); | |
| } | |
| for (i = 0; i < entriesToRemove.length; i++) { | |
| noteholder.removeChild(entriesToRemove[i]); | |
| } | |
| // Rebuild footnote entries. | |
| var cont = document.getElementById("content"); | |
| var spans = cont.getElementsByTagName("span"); | |
| var refs = {}; | |
| var n = 0; | |
| for (i=0; i<spans.length; i++) { | |
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| n++; | |
| var note = spans[i].getAttribute("data-note"); | |
| if (!note) { | |
| // Use [\s\S] in place of . so multi-line matches work. | |
| // Because JavaScript has no s (dotall) regex flag. | |
| note = spans[i].innerHTML.match(/\s*\[([\s\S]*)]\s*/)[1]; | |
| spans[i].innerHTML = | |
| "[<a id='_footnoteref_" + n + "' href='#_footnote_" + n + | |
| "' title='View footnote' class='footnote'>" + n + "</a>]"; | |
| spans[i].setAttribute("data-note", note); | |
| } | |
| noteholder.innerHTML += | |
| "<div class='footnote' id='_footnote_" + n + "'>" + | |
| "<a href='#_footnoteref_" + n + "' title='Return to text'>" + | |
| n + "</a>. " + note + "</div>"; | |
| var id =spans[i].getAttribute("id"); | |
| if (id != null) refs["#"+id] = n; | |
| } | |
| } | |
| if (n == 0) | |
| noteholder.parentNode.removeChild(noteholder); | |
| else { | |
| // Process footnoterefs. | |
| for (i=0; i<spans.length; i++) { | |
| if (spans[i].className == "footnoteref") { | |
| var href = spans[i].getElementsByTagName("a")[0].getAttribute("href"); | |
| href = href.match(/#.*/)[0]; // Because IE return full URL. | |
| n = refs[href]; | |
| spans[i].innerHTML = | |
| "[<a href='#_footnote_" + n + | |
| "' title='View footnote' class='footnote'>" + n + "</a>]"; | |
| } | |
| } | |
| } | |
| }, | |
| install: function(toclevels) { | |
| var timerId; | |
| function reinstall() { | |
| asciidoc.footnotes(); | |
| if (toclevels) { | |
| asciidoc.toc(toclevels); | |
| } | |
| } | |
| function reinstallAndRemoveTimer() { | |
| clearInterval(timerId); | |
| reinstall(); | |
| } | |
| timerId = setInterval(reinstall, 500); | |
| if (document.addEventListener) | |
| document.addEventListener("DOMContentLoaded", reinstallAndRemoveTimer, false); | |
| else | |
| window.onload = reinstallAndRemoveTimer; | |
| } | |
| } | |
| asciidoc.install(); | |
| /*]]>*/ | |
| </script> | |
| </head> | |
| <body class="manpage"> | |
| <div id="header"> | |
| <h1> | |
| gitformat-commit-graph(5) Manual Page | |
| </h1> | |
| <h2>NAME</h2> | |
| <div class="sectionbody"> | |
| <p>gitformat-commit-graph - | |
| Git commit-graph format | |
| </p> | |
| </div> | |
| </div> | |
| <div id="content"> | |
| <div class="sect1"> | |
| <h2 id="_synopsis">SYNOPSIS</h2> | |
| <div class="sectionbody"> | |
| <div class="verseblock"> | |
| <pre class="content">$GIT_DIR/objects/info/commit-graph | |
| $GIT_DIR/objects/info/commit-graphs/*</pre> | |
| <div class="attribution"> | |
| </div></div> | |
| </div> | |
| </div> | |
| <div class="sect1"> | |
| <h2 id="_description">DESCRIPTION</h2> | |
| <div class="sectionbody"> | |
| <div class="paragraph"><p>The Git commit-graph stores a list of commit OIDs and some associated | |
| metadata, including:</p></div> | |
| <div class="ulist"><ul> | |
| <li> | |
| <p> | |
| The generation number of the commit. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The root tree OID. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The commit date. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The parents of the commit, stored using positional references within | |
| the graph file. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The Bloom filter of the commit carrying the paths that were changed between | |
| the commit and its first parent, if requested. | |
| </p> | |
| </li> | |
| </ul></div> | |
| <div class="paragraph"><p>These positional references are stored as unsigned 32-bit integers | |
| corresponding to the array position within the list of commit OIDs. Due | |
| to some special constants we use to track parents, we can store at most | |
| (1 << 30) + (1 << 29) + (1 << 28) - 1 (around 1.8 billion) commits.</p></div> | |
| </div> | |
| </div> | |
| <div class="sect1"> | |
| <h2 id="_commit_graph_files_have_the_following_format">Commit-graph files have the following format:</h2> | |
| <div class="sectionbody"> | |
| <div class="paragraph"><p>In order to allow extensions that add extra data to the graph, we organize | |
| the body into "chunks" and provide a binary lookup table at the beginning | |
| of the body. The header includes certain values, such as number of chunks | |
| and hash type.</p></div> | |
| <div class="paragraph"><p>All multi-byte numbers are in network byte order.</p></div> | |
| <div class="sect2"> | |
| <h3 id="_header">HEADER:</h3> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>4-byte signature: | |
| The signature is: {'C', 'G', 'P', 'H'}</code></pre> | |
| </div></div> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>1-byte version number: | |
| Currently, the only valid version is 1.</code></pre> | |
| </div></div> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>1-byte Hash Version | |
| We infer the hash length (H) from this value: | |
| 1 => SHA-1 | |
| 2 => SHA-256 | |
| If the hash type does not match the repository's hash algorithm, the | |
| commit-graph file should be ignored with a warning presented to the | |
| user.</code></pre> | |
| </div></div> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>1-byte number (C) of "chunks"</code></pre> | |
| </div></div> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>1-byte number (B) of base commit-graphs | |
| We infer the length (H*B) of the Base Graphs chunk | |
| from this value.</code></pre> | |
| </div></div> | |
| </div> | |
| <div class="sect2"> | |
| <h3 id="_chunk_lookup">CHUNK LOOKUP:</h3> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>(C + 1) * 12 bytes listing the table of contents for the chunks: | |
| First 4 bytes describe the chunk id. Value 0 is a terminating label. | |
| Other 8 bytes provide the byte-offset in current file for chunk to | |
| start. (Chunks are ordered contiguously in the file, so you can infer | |
| the length using the next chunk position if necessary.) Each chunk | |
| ID appears at most once.</code></pre> | |
| </div></div> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>The CHUNK LOOKUP matches the table of contents from | |
| the chunk-based file format, see linkgit:gitformat-chunk[5]</code></pre> | |
| </div></div> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>The remaining data in the body is described one chunk at a time, and | |
| these chunks may be given in any order. Chunks are required unless | |
| otherwise specified.</code></pre> | |
| </div></div> | |
| </div> | |
| <div class="sect2"> | |
| <h3 id="_chunk_data">CHUNK DATA:</h3> | |
| <div class="sect3"> | |
| <h4 id="_oid_fanout_id_em_o_em_em_i_em_em_d_em_em_f_em_256_4_bytes">OID Fanout (ID: {<em>O</em>, <em>I</em>, <em>D</em>, <em>F</em>}) (256 * 4 bytes)</h4> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>The ith entry, F[i], stores the number of OIDs with first | |
| byte at most i. Thus F[255] stores the total | |
| number of commits (N).</code></pre> | |
| </div></div> | |
| </div> | |
| <div class="sect3"> | |
| <h4 id="_oid_lookup_id_em_o_em_em_i_em_em_d_em_em_l_em_n_h_bytes">OID Lookup (ID: {<em>O</em>, <em>I</em>, <em>D</em>, <em>L</em>}) (N * H bytes)</h4> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>The OIDs for all commits in the graph, sorted in ascending order.</code></pre> | |
| </div></div> | |
| </div> | |
| <div class="sect3"> | |
| <h4 id="_commit_data_id_em_c_em_em_d_em_em_a_em_em_t_em_n_h_16_bytes">Commit Data (ID: {<em>C</em>, <em>D</em>, <em>A</em>, <em>T</em> }) (N * (H + 16) bytes)</h4> | |
| <div class="ulist"><ul> | |
| <li> | |
| <p> | |
| The first H bytes are for the OID of the root tree. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The next 8 bytes are for the positions of the first two parents | |
| of the ith commit. Stores value 0x70000000 if no parent in that | |
| position. If there are more than two parents, the second value | |
| has its most-significant bit on and the other bits store an array | |
| position into the Extra Edge List chunk. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The next 8 bytes store the topological level (generation number v1) | |
| of the commit and | |
| the commit time in seconds since EPOCH. The generation number | |
| uses the higher 30 bits of the first 4 bytes, while the commit | |
| time uses the 32 bits of the second 4 bytes, along with the lowest | |
| 2 bits of the lowest byte, storing the 33rd and 34th bit of the | |
| commit time. | |
| </p> | |
| </li> | |
| </ul></div> | |
| </div> | |
| <div class="sect3"> | |
| <h4 id="_generation_data_id_em_g_em_em_d_em_em_a_em_em_2_em_n_4_bytes_optional">Generation Data (ID: {<em>G</em>, <em>D</em>, <em>A</em>, <em>2</em> }) (N * 4 bytes) [Optional]</h4> | |
| <div class="ulist"><ul> | |
| <li> | |
| <p> | |
| This list of 4-byte values store corrected commit date offsets for the | |
| commits, arranged in the same order as commit data chunk. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| If the corrected commit date offset cannot be stored within 31 bits, | |
| the value has its most-significant bit on and the other bits store | |
| the position of corrected commit date into the Generation Data Overflow | |
| chunk. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| Generation Data chunk is present only when commit-graph file is written | |
| by compatible versions of Git and in case of split commit-graph chains, | |
| the topmost layer also has Generation Data chunk. | |
| </p> | |
| </li> | |
| </ul></div> | |
| </div> | |
| <div class="sect3"> | |
| <h4 id="_generation_data_overflow_id_em_g_em_em_d_em_em_o_em_em_2_em_optional">Generation Data Overflow (ID: {<em>G</em>, <em>D</em>, <em>O</em>, <em>2</em> }) [Optional]</h4> | |
| <div class="ulist"><ul> | |
| <li> | |
| <p> | |
| This list of 8-byte values stores the corrected commit date offsets | |
| for commits with corrected commit date offsets that cannot be | |
| stored within 31 bits. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| Generation Data Overflow chunk is present only when Generation Data | |
| chunk is present and atleast one corrected commit date offset cannot | |
| be stored within 31 bits. | |
| </p> | |
| </li> | |
| </ul></div> | |
| </div> | |
| <div class="sect3"> | |
| <h4 id="_extra_edge_list_id_em_e_em_em_d_em_em_g_em_em_e_em_optional">Extra Edge List (ID: {<em>E</em>, <em>D</em>, <em>G</em>, <em>E</em>}) [Optional]</h4> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>This list of 4-byte values store the second through nth parents for | |
| all octopus merges. The second parent value in the commit data stores | |
| an array position within this list along with the most-significant bit | |
| on. Starting at that array position, iterate through this list of commit | |
| positions for the parents until reaching a value with the most-significant | |
| bit on. The other bits correspond to the position of the last parent.</code></pre> | |
| </div></div> | |
| </div> | |
| <div class="sect3"> | |
| <h4 id="_bloom_filter_index_id_em_b_em_em_i_em_em_d_em_em_x_em_n_4_bytes_optional">Bloom Filter Index (ID: {<em>B</em>, <em>I</em>, <em>D</em>, <em>X</em>}) (N * 4 bytes) [Optional]</h4> | |
| <div class="ulist"><ul> | |
| <li> | |
| <p> | |
| The ith entry, BIDX[i], stores the number of bytes in all Bloom filters | |
| from commit 0 to commit i (inclusive) in lexicographic order. The Bloom | |
| filter for the i-th commit spans from BIDX[i-1] to BIDX[i] (plus header | |
| length), where BIDX[-1] is 0. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The BIDX chunk is ignored if the BDAT chunk is not present. | |
| </p> | |
| </li> | |
| </ul></div> | |
| </div> | |
| <div class="sect3"> | |
| <h4 id="_bloom_filter_data_id_em_b_em_em_d_em_em_a_em_em_t_em_optional">Bloom Filter Data (ID: {<em>B</em>, <em>D</em>, <em>A</em>, <em>T</em>}) [Optional]</h4> | |
| <div class="ulist"><ul> | |
| <li> | |
| <p> | |
| It starts with header consisting of three unsigned 32-bit integers: | |
| </p> | |
| <div class="ulist"><ul> | |
| <li> | |
| <p> | |
| Version of the hash algorithm being used. We currently only support | |
| value 1 which corresponds to the 32-bit version of the murmur3 hash | |
| implemented exactly as described in | |
| <a href="https://en.wikipedia.org/wiki/MurmurHash#Algorithm">https://en.wikipedia.org/wiki/MurmurHash#Algorithm</a> and the double | |
| hashing technique using seed values 0x293ae76f and 0x7e646e2 as | |
| described in <a href="https://doi.org/10.1007/978-3-540-30494-4_26">https://doi.org/10.1007/978-3-540-30494-4_26</a> "Bloom Filters | |
| in Probabilistic Verification" | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The number of times a path is hashed and hence the number of bit positions | |
| that cumulatively determine whether a file is present in the commit. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The minimum number of bits <em>b</em> per entry in the Bloom filter. If the filter | |
| contains <em>n</em> entries, then the filter size is the minimum number of 64-bit | |
| words that contain n*b bits. | |
| </p> | |
| </li> | |
| </ul></div> | |
| </li> | |
| <li> | |
| <p> | |
| The rest of the chunk is the concatenation of all the computed Bloom | |
| filters for the commits in lexicographic order. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| Note: Commits with no changes or more than 512 changes have Bloom filters | |
| of length one, with either all bits set to zero or one respectively. | |
| </p> | |
| </li> | |
| <li> | |
| <p> | |
| The BDAT chunk is present if and only if BIDX is present. | |
| </p> | |
| </li> | |
| </ul></div> | |
| </div> | |
| <div class="sect3"> | |
| <h4 id="_base_graphs_list_id_em_b_em_em_a_em_em_s_em_em_e_em_optional">Base Graphs List (ID: {<em>B</em>, <em>A</em>, <em>S</em>, <em>E</em>}) [Optional]</h4> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>This list of H-byte hashes describe a set of B commit-graph files that | |
| form a commit-graph chain. The graph position for the ith commit in this | |
| file's OID Lookup chunk is equal to i plus the number of commits in all | |
| base graphs. If B is non-zero, this chunk must exist.</code></pre> | |
| </div></div> | |
| </div> | |
| </div> | |
| <div class="sect2"> | |
| <h3 id="_trailer">TRAILER:</h3> | |
| <div class="literalblock"> | |
| <div class="content"> | |
| <pre><code>H-byte HASH-checksum of all of the above.</code></pre> | |
| </div></div> | |
| </div> | |
| </div> | |
| </div> | |
| <div class="sect1"> | |
| <h2 id="_historical_notes">Historical Notes:</h2> | |
| <div class="sectionbody"> | |
| <div class="paragraph"><p>The Generation Data (GDA2) and Generation Data Overflow (GDO2) chunks have | |
| the number <em>2</em> in their chunk IDs because a previous version of Git wrote | |
| possibly erroneous data in these chunks with the IDs "GDAT" and "GDOV". By | |
| changing the IDs, newer versions of Git will silently ignore those older | |
| chunks and write the new information without trusting the incorrect data.</p></div> | |
| </div> | |
| </div> | |
| <div class="sect1"> | |
| <h2 id="_git">GIT</h2> | |
| <div class="sectionbody"> | |
| <div class="paragraph"><p>Part of the <a href="git.html">git(1)</a> suite</p></div> | |
| </div> | |
| </div> | |
| </div> | |
| <div id="footnotes"><hr /></div> | |
| <div id="footer"> | |
| <div id="footer-text"> | |
| Last updated | |
| 2022-11-11 23:55:30 PST | |
| </div> | |
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