technical/bitmap-format.html

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   8 <title>GIT bitmap v1 format</title>
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 435 </head>
 436 <body class="article">
 437 <div id="header">
 438 <h1>GIT bitmap v1 format</h1>
 439 <div class="details">
 440 <span id="revdate">2024-10-02</span>
 441 </div>
 442 </div>
 443 <div id="content">
 444 <div class="sect1">
 445 <h2 id="_pack_and_multi_pack_bitmaps">Pack and multi-pack bitmaps</h2>
 446 <div class="sectionbody">
 447 <div class="paragraph">
 448 <p>Bitmaps store reachability information about the set of objects in a packfile,
 449 or a multi-pack index (MIDX). The former is defined obviously, and the latter is
 450 defined as the union of objects in packs contained in the MIDX.</p>
 451 </div>
 452 <div class="paragraph">
 453 <p>A bitmap may belong to either one pack, or the repository&#8217;s multi-pack index (if
 454 it exists). A repository may have at most one bitmap.</p>
 455 </div>
 456 <div class="paragraph">
 457 <p>An object is uniquely described by its bit position within a bitmap:</p>
 458 </div>
 459 <div class="ulist">
 460 <ul>
 461 <li>
 462 <p>If the bitmap belongs to a packfile, the <em>n</em>th bit corresponds to
 463 the <em>n</em>th object in pack order. For a function <code>offset</code> which maps
 464 objects to their byte offset within a pack, pack order is defined as
 465 follows:</p>
 466 <div class="literalblock">
 467 <div class="content">
 468 <pre>o1 &lt;= o2 &lt;==&gt; offset(o1) &lt;= offset(o2)</pre>
 469 </div>
 470 </div>
 471 </li>
 472 <li>
 473 <p>If the bitmap belongs to a MIDX, the <em>n</em>th bit corresponds to the
 474 <em>n</em>th object in MIDX order. With an additional function <code>pack</code> which
 475 maps objects to the pack they were selected from by the MIDX, MIDX order
 476 is defined as follows:</p>
 477 <div class="literalblock">
 478 <div class="content">
 479 <pre>o1 &lt;= o2 &lt;==&gt; pack(o1) &lt;= pack(o2) /\ offset(o1) &lt;= offset(o2)</pre>
 480 </div>
 481 </div>
 482 <div class="paragraph">
 483 <p>The ordering between packs is done according to the MIDX&#8217;s .rev file.
 484 Notably, the preferred pack sorts ahead of all other packs.</p>
 485 </div>
 486 </li>
 487 </ul>
 488 </div>
 489 <div class="paragraph">
 490 <p>The on-disk representation (described below) of a bitmap is the same regardless
 491 of whether or not that bitmap belongs to a packfile or a MIDX. The only
 492 difference is the interpretation of the bits, which is described above.</p>
 493 </div>
 494 <div class="paragraph">
 495 <p>Certain bitmap extensions are supported (see: Appendix B). No extensions are
 496 required for bitmaps corresponding to packfiles. For bitmaps that correspond to
 497 MIDXs, both the bit-cache and rev-cache extensions are required.</p>
 498 </div>
 499 </div>
 500 </div>
 501 <div class="sect1">
 502 <h2 id="_on_disk_format">On-disk format</h2>
 503 <div class="sectionbody">
 504 <div class="ulist">
 505 <ul>
 506 <li>
 507 <p>A header appears at the beginning:</p>
 508 <div class="dlist">
 509 <dl>
 510 <dt class="hdlist1">4-byte signature: </dt>
 511 <dd>
 512 <p>{<em>B</em>, <em>I</em>, <em>T</em>, <em>M</em>}</p>
 513 </dd>
 514 <dt class="hdlist1">2-byte version number (network byte order): </dt>
 515 <dd>
 516 <p>The current implementation only supports version 1
 517 of the bitmap index (the same one as JGit).</p>
 518 </dd>
 519 <dt class="hdlist1">2-byte flags (network byte order): </dt>
 520 <dd>
 521 <p>The following flags are supported:</p>
 522 <div class="ulist">
 523 <ul>
 524 <li>
 525 <p></p>
 526 <div class="dlist">
 527 <dl>
 528 <dt class="hdlist1">BITMAP_OPT_FULL_DAG (0x1) REQUIRED: </dt>
 529 <dd>
 530 <p>This flag must always be present. It implies that the
 531 bitmap index has been generated for a packfile or
 532 multi-pack index (MIDX) with full closure (i.e. where
 533 every single object in the packfile/MIDX can find its
 534 parent links inside the same packfile/MIDX). This is a
 535 requirement for the bitmap index format, also present in
 536 JGit, that greatly reduces the complexity of the
 537 implementation.</p>
 538 </dd>
 539 </dl>
 540 </div>
 541 </li>
 542 <li>
 543 <p></p>
 544 <div class="dlist">
 545 <dl>
 546 <dt class="hdlist1">BITMAP_OPT_HASH_CACHE (0x4): </dt>
 547 <dd>
 548 <p>If present, the end of the bitmap file contains
 549 <code>N</code> 32-bit name-hash values, one per object in the
 550 pack/MIDX. The format and meaning of the name-hash is
 551 described below.</p>
 552 </dd>
 553 </dl>
 554 </div>
 555 </li>
 556 <li>
 557 <p></p>
 558 <div class="dlist">
 559 <dl>
 560 <dt class="hdlist1">BITMAP_OPT_LOOKUP_TABLE (0x10): </dt>
 561 <dd>
 562 <p>If present, the end of the bitmap file contains a table
 563 containing a list of <code>N</code> &lt;commit_pos, offset, xor_row&gt;
 564 triplets. The format and meaning of the table is described
 565 below.</p>
 566 <div class="admonitionblock note">
 567 <table>
 568 <tr>
 569 <td class="icon">
 570 <div class="title">Note</div>
 571 </td>
 572 <td class="content">
 573 Unlike the xor_offset used to compress an individual bitmap,
 574 <code>xor_row</code> stores an <strong>absolute</strong> index into the lookup table, not a location
 575 relative to the current entry.
 576 </td>
 577 </tr>
 578 </table>
 579 </div>
 580 </dd>
 581 </dl>
 582 </div>
 583 </li>
 584 </ul>
 585 </div>
 586 </dd>
 587 <dt class="hdlist1">4-byte entry count (network byte order): </dt>
 588 <dd>
 589 <p>The total count of entries (bitmapped commits) in this bitmap index.</p>
 590 </dd>
 591 <dt class="hdlist1">20-byte checksum: </dt>
 592 <dd>
 593 <p>The SHA1 checksum of the pack/MIDX this bitmap index
 594 belongs to.</p>
 595 </dd>
 596 </dl>
 597 </div>
 598 </li>
 599 <li>
 600 <p>4 EWAH bitmaps that act as type indexes</p>
 601 <div class="paragraph">
 602 <p>Type indexes are serialized after the hash cache in the shape
 603 of four EWAH bitmaps stored consecutively (see Appendix A for
 604 the serialization format of an EWAH bitmap).</p>
 605 </div>
 606 <div class="paragraph">
 607 <p>There is a bitmap for each Git object type, stored in the following
 608 order:</p>
 609 </div>
 610 <div class="ulist">
 611 <ul>
 612 <li>
 613 <p>Commits</p>
 614 </li>
 615 <li>
 616 <p>Trees</p>
 617 </li>
 618 <li>
 619 <p>Blobs</p>
 620 </li>
 621 <li>
 622 <p>Tags</p>
 623 </li>
 624 </ul>
 625 </div>
 626 <div class="paragraph">
 627 <p>In each bitmap, the `n`th bit is set to true if the `n`th object
 628 in the packfile or multi-pack index is of that type.</p>
 629 </div>
 630 <div class="paragraph">
 631 <p>The obvious consequence is that the OR of all 4 bitmaps will result
 632 in a full set (all bits set), and the AND of all 4 bitmaps will
 633 result in an empty bitmap (no bits set).</p>
 634 </div>
 635 </li>
 636 <li>
 637 <p>N entries with compressed bitmaps, one for each indexed commit</p>
 638 <div class="paragraph">
 639 <p>Where <code>N</code> is the total number of entries in this bitmap index.
 640 Each entry contains the following:</p>
 641 </div>
 642 <div class="ulist">
 643 <ul>
 644 <li>
 645 <p></p>
 646 <div class="dlist">
 647 <dl>
 648 <dt class="hdlist1">4-byte object position (network byte order): </dt>
 649 <dd>
 650 <p>The position <strong>in the index for the packfile or
 651 multi-pack index</strong> where the bitmap for this commit is
 652 found.</p>
 653 </dd>
 654 </dl>
 655 </div>
 656 </li>
 657 <li>
 658 <p></p>
 659 <div class="dlist">
 660 <dl>
 661 <dt class="hdlist1">1-byte XOR-offset: </dt>
 662 <dd>
 663 <p>The xor offset used to compress this bitmap. For an entry
 664 in position <code>x</code>, an XOR offset of <code>y</code> means that the actual
 665 bitmap representing this commit is composed by XORing the
 666 bitmap for this entry with the bitmap in entry <code>x-y</code> (i.e.
 667 the bitmap <code>y</code> entries before this one).</p>
 668 <div class="admonitionblock note">
 669 <table>
 670 <tr>
 671 <td class="icon">
 672 <div class="title">Note</div>
 673 </td>
 674 <td class="content">
 675 This compression can be recursive. In order to
 676 XOR this entry with a previous one, the previous entry needs
 677 to be decompressed first, and so on.
 678 </td>
 679 </tr>
 680 </table>
 681 </div>
 682 <div class="paragraph">
 683 <p>The hard-limit for this offset is 160 (an entry can only be
 684 xor&#8217;ed against one of the 160 entries preceding it). This
 685 number is always positive, and hence entries are always xor&#8217;ed
 686 with <strong>previous</strong> bitmaps, not bitmaps that will come afterwards
 687 in the index.</p>
 688 </div>
 689 </dd>
 690 </dl>
 691 </div>
 692 </li>
 693 <li>
 694 <p></p>
 695 <div class="dlist">
 696 <dl>
 697 <dt class="hdlist1">1-byte flags for this bitmap: </dt>
 698 <dd>
 699 <p>At the moment the only available flag is <code>0x1</code>, which hints
 700 that this bitmap can be re-used when rebuilding bitmap indexes
 701 for the repository.</p>
 702 </dd>
 703 </dl>
 704 </div>
 705 </li>
 706 <li>
 707 <p>The compressed bitmap itself, see Appendix A.</p>
 708 </li>
 709 </ul>
 710 </div>
 711 </li>
 712 <li>
 713 <p></p>
 714 <div class="dlist">
 715 <dl>
 716 <dt class="hdlist1">TRAILER: </dt>
 717 <dd>
 718 <p>Trailing checksum of the preceding contents.</p>
 719 </dd>
 720 </dl>
 721 </div>
 722 </li>
 723 </ul>
 724 </div>
 725 </div>
 726 </div>
 727 <div class="sect1">
 728 <h2 id="_appendix_a_serialization_format_for_an_ewah_bitmap">Appendix A: Serialization format for an EWAH bitmap</h2>
 729 <div class="sectionbody">
 730 <div class="paragraph">
 731 <p>Ewah bitmaps are serialized in the same protocol as the JAVAEWAH
 732 library, making them backwards compatible with the JGit
 733 implementation:</p>
 734 </div>
 735 <div class="ulist">
 736 <ul>
 737 <li>
 738 <p>4-byte number of bits of the resulting UNCOMPRESSED bitmap</p>
 739 </li>
 740 <li>
 741 <p>4-byte number of words of the COMPRESSED bitmap, when stored</p>
 742 </li>
 743 <li>
 744 <p>N x 8-byte words, as specified by the previous field</p>
 745 <div class="paragraph">
 746 <p>This is the actual content of the compressed bitmap.</p>
 747 </div>
 748 </li>
 749 <li>
 750 <p>4-byte position of the current RLW for the compressed
 751 bitmap</p>
 752 </li>
 753 </ul>
 754 </div>
 755 <div class="paragraph">
 756 <p>All words are stored in network byte order for their corresponding
 757 sizes.</p>
 758 </div>
 759 <div class="paragraph">
 760 <p>The compressed bitmap is stored in a form of run-length encoding, as
 761 follows.  It consists of a concatenation of an arbitrary number of
 762 chunks.  Each chunk consists of one or more 64-bit words</p>
 763 </div>
 764 <div class="literalblock">
 765 <div class="content">
 766 <pre>H  L_1  L_2  L_3 .... L_M</pre>
 767 </div>
 768 </div>
 769 <div class="paragraph">
 770 <p>H is called RLW (run length word).  It consists of (from lower to higher
 771 order bits):</p>
 772 </div>
 773 <div class="ulist">
 774 <ul>
 775 <li>
 776 <p>1 bit: the repeated bit B</p>
 777 </li>
 778 <li>
 779 <p>32 bits: repetition count K (unsigned)</p>
 780 </li>
 781 <li>
 782 <p>31 bits: literal word count M (unsigned)</p>
 783 </li>
 784 </ul>
 785 </div>
 786 <div class="paragraph">
 787 <p>The bitstream represented by the above chunk is then:</p>
 788 </div>
 789 <div class="ulist">
 790 <ul>
 791 <li>
 792 <p>K repetitions of B</p>
 793 </li>
 794 <li>
 795 <p>The bits stored in <code>L_1</code> through <code>L_M</code>.  Within a word, bits at
 796 lower order come earlier in the stream than those at higher
 797 order.</p>
 798 </li>
 799 </ul>
 800 </div>
 801 <div class="paragraph">
 802 <p>The next word after <code>L_M</code> (if any) must again be a RLW, for the next
 803 chunk.  For efficient appending to the bitstream, the EWAH stores a
 804 pointer to the last RLW in the stream.</p>
 805 </div>
 806 </div>
 807 </div>
 808 <div class="sect1">
 809 <h2 id="_appendix_b_optional_bitmap_sections">Appendix B: Optional Bitmap Sections</h2>
 810 <div class="sectionbody">
 811 <div class="paragraph">
 812 <p>These sections may or may not be present in the <code>.bitmap</code> file; their
 813 presence is indicated by the header flags section described above.</p>
 814 </div>
 815 </div>
 816 </div>
 817 <div class="sect1">
 818 <h2 id="_name_hash_cache">Name-hash cache</h2>
 819 <div class="sectionbody">
 820 <div class="paragraph">
 821 <p>If the BITMAP_OPT_HASH_CACHE flag is set, the end of the bitmap contains
 822 a cache of 32-bit values, one per object in the pack/MIDX. The value at
 823 position <code>i</code> is the hash of the pathname at which the `i`th object
 824 (counting in index or multi-pack index order) in the pack/MIDX can be found.
 825 This can be fed into the delta heuristics to compare objects with similar
 826 pathnames.</p>
 827 </div>
 828 <div class="paragraph">
 829 <p>The hash algorithm used is:</p>
 830 </div>
 831 <div class="literalblock">
 832 <div class="content">
 833 <pre>hash = 0;
 834 while ((c = *name++))
 835  if (!isspace(c))
 836   hash = (hash &gt;&gt; 2) + (c &lt;&lt; 24);</pre>
 837 </div>
 838 </div>
 839 <div class="paragraph">
 840 <p>Note that this hashing scheme is tied to the BITMAP_OPT_HASH_CACHE flag.
 841 If implementations want to choose a different hashing scheme, they are
 842 free to do so, but MUST allocate a new header flag (because comparing
 843 hashes made under two different schemes would be pointless).</p>
 844 </div>
 845 </div>
 846 </div>
 847 <div class="sect1">
 848 <h2 id="_commit_lookup_table">Commit lookup table</h2>
 849 <div class="sectionbody">
 850 <div class="paragraph">
 851 <p>If the BITMAP_OPT_LOOKUP_TABLE flag is set, the last <code>N * (4 + 8 + 4)</code>
 852 bytes (preceding the name-hash cache and trailing hash) of the <code>.bitmap</code>
 853 file contains a lookup table specifying the information needed to get
 854 the desired bitmap from the entries without parsing previous unnecessary
 855 bitmaps.</p>
 856 </div>
 857 <div class="paragraph">
 858 <p>For a <code>.bitmap</code> containing <code>nr_entries</code> reachability bitmaps, the table
 859 contains a list of <code>nr_entries</code> &lt;commit_pos, offset, xor_row&gt; triplets
 860 (sorted in the ascending order of <code>commit_pos</code>). The content of the i&#8217;th
 861 triplet is -</p>
 862 </div>
 863 <div class="ulist">
 864 <ul>
 865 <li>
 866 <p></p>
 867 <div class="dlist">
 868 <dl>
 869 <dt class="hdlist1">commit_pos (4 byte integer, network byte order): </dt>
 870 <dd>
 871 <p>It stores the object position of a commit (in the midx or pack
 872 index).</p>
 873 </dd>
 874 </dl>
 875 </div>
 876 </li>
 877 <li>
 878 <p></p>
 879 <div class="dlist">
 880 <dl>
 881 <dt class="hdlist1">offset (8 byte integer, network byte order): </dt>
 882 <dd>
 883 <p>The offset from which that commit&#8217;s bitmap can be read.</p>
 884 </dd>
 885 </dl>
 886 </div>
 887 </li>
 888 <li>
 889 <p></p>
 890 <div class="dlist">
 891 <dl>
 892 <dt class="hdlist1">xor_row (4 byte integer, network byte order): </dt>
 893 <dd>
 894 <p>The position of the triplet whose bitmap is used to compress
 895 this one, or <code>0xffffffff</code> if no such bitmap exists.</p>
 896 </dd>
 897 </dl>
 898 </div>
 899 </li>
 900 </ul>
 901 </div>
 902 </div>
 903 </div>
 904 <div class="sect1">
 905 <h2 id="_pseudo_merge_bitmaps">Pseudo-merge bitmaps</h2>
 906 <div class="sectionbody">
 907 <div class="paragraph">
 908 <p>If the <code>BITMAP_OPT_PSEUDO_MERGES</code> flag is set, a variable number of
 909 bytes (preceding the name-hash cache, commit lookup table, and trailing
 910 checksum) of the <code>.bitmap</code> file is used to store pseudo-merge bitmaps.</p>
 911 </div>
 912 <div class="paragraph">
 913 <p>For more information on what pseudo-merges are, why they are useful, and
 914 how to configure them, see the information in <a href="../gitpacking.html">gitpacking(7)</a>.</p>
 915 </div>
 916 <div class="sect2">
 917 <h3 id="_file_format">File format</h3>
 918 <div class="paragraph">
 919 <p>If enabled, pseudo-merge bitmaps are stored in an optional section at
 920 the end of a <code>.bitmap</code> file. The format is as follows:</p>
 921 </div>
 922 <div class="literalblock">
 923 <div class="content">
 924 <pre>+-------------------------------------------+
 925 |               .bitmap File                |
 926 +-------------------------------------------+
 927 |                                           |
 928 |  Pseudo-merge bitmaps (Variable Length)   |
 929 |  +---------------------------+            |
 930 |  | commits_bitmap (EWAH)     |            |
 931 |  +---------------------------+            |
 932 |  | merge_bitmap (EWAH)       |            |
 933 |  +---------------------------+            |
 934 |                                           |
 935 +-------------------------------------------+
 936 |                                           |
 937 |  Lookup Table                             |
 938 |  +---------------------------+            |
 939 |  | commit_pos (4 bytes)      |            |
 940 |  +---------------------------+            |
 941 |  | offset (8 bytes)          |            |
 942 |  +------------+--------------+            |
 943 |                                           |
 944 |  Offset Cases:                            |
 945 |  -------------                            |
 946 |                                           |
 947 |  1. MSB Unset: single pseudo-merge bitmap |
 948 |     + offset to pseudo-merge bitmap       |
 949 |                                           |
 950 |  2. MSB Set: multiple pseudo-merges       |
 951 |     + offset to extended lookup table     |
 952 |                                           |
 953 +-------------------------------------------+
 954 |                                           |
 955 |  Extended Lookup Table (Optional)         |
 956 |  +----+----------+----------+----------+  |
 957 |  | N  | Offset 1 |   ....   | Offset N |  |
 958 |  +----+----------+----------+----------+  |
 959 |  |    |  8 bytes |   ....   |  8 bytes |  |
 960 |  +----+----------+----------+----------+  |
 961 |                                           |
 962 +-------------------------------------------+
 963 |                                           |
 964 |  Pseudo-merge position table              |
 965 |  +----+----------+----------+----------+  |
 966 |  | N  | Offset 1 |   ....   | Offset N |  |
 967 |  +----+----------+----------+----------+  |
 968 |  |    |  8 bytes |   ....   |  8 bytes |  |
 969 |  +----+----------+----------+----------+  |
 970 |                                           |
 971 +-------------------------------------------+
 972 |                                           |
 973 |  Pseudo-merge Metadata                    |
 974 |  +-----------------------------------+    |
 975 |  | # pseudo-merges (4 bytes)         |    |
 976 |  +-----------------------------------+    |
 977 |  | # commits (4 bytes)               |    |
 978 |  +-----------------------------------+    |
 979 |  | Lookup offset (8 bytes)           |    |
 980 |  +-----------------------------------+    |
 981 |  | Extension size (8 bytes)          |    |
 982 |  +-----------------------------------+    |
 983 |                                           |
 984 +-------------------------------------------+</pre>
 985 </div>
 986 </div>
 987 <div class="ulist">
 988 <ul>
 989 <li>
 990 <p>One or more pseudo-merge bitmaps, each containing:</p>
 991 <div class="ulist">
 992 <ul>
 993 <li>
 994 <p><code>commits_bitmap</code>, an EWAH-compressed bitmap describing the set of
 995 commits included in the this psuedo-merge.</p>
 996 </li>
 997 <li>
 998 <p><code>merge_bitmap</code>, an EWAH-compressed bitmap describing the union of
 999 the set of objects reachable from all commits listed in the
1000 <code>commits_bitmap</code>.</p>
1001 </li>
1002 </ul>
1003 </div>
1004 </li>
1005 <li>
1006 <p>A lookup table, mapping pseudo-merged commits to the pseudo-merges
1007 they belong to. Entries appear in increasing order of each commit&#8217;s
1008 bit position. Each entry is 12 bytes wide, and is comprised of the
1009 following:</p>
1010 <div class="ulist">
1011 <ul>
1012 <li>
1013 <p><code>commit_pos</code>, a 4-byte unsigned value (in network byte-order)
1014 containing the bit position for this commit.</p>
1015 </li>
1016 <li>
1017 <p><code>offset</code>, an 8-byte unsigned value (also in network byte-order)
1018 containing either one of two possible offsets, depending on whether or
1019 not the most-significant bit is set.</p>
1020 <div class="ulist">
1021 <ul>
1022 <li>
1023 <p>If unset (i.e. <code>offset &amp; ((uint64_t)1&lt;&lt;63) == 0</code>), the offset
1024 (relative to the beginning of the <code>.bitmap</code> file) at which the
1025 pseudo-merge bitmap for this commit can be read. This indicates
1026 only a single pseudo-merge bitmap contains this commit.</p>
1027 </li>
1028 <li>
1029 <p>If set (i.e. <code>offset &amp; ((uint64_t)1&lt;&lt;63) != 0</code>), the offset
1030 (again relative to the beginning of the <code>.bitmap</code> file) at which
1031 the extended offset table can be located describing the set of
1032 pseudo-merge bitmaps which contain this commit. This indicates
1033 that multiple pseudo-merge bitmaps contain this commit.</p>
1034 </li>
1035 </ul>
1036 </div>
1037 </li>
1038 </ul>
1039 </div>
1040 </li>
1041 <li>
1042 <p>An (optional) extended lookup table (written if and only if there is
1043 at least one commit which appears in more than one pseudo-merge).
1044 There are as many entries as commits which appear in multiple
1045 pseudo-merges. Each entry contains the following:</p>
1046 <div class="ulist">
1047 <ul>
1048 <li>
1049 <p><code>N</code>, a 4-byte unsigned value equal to the number of pseudo-merges
1050 which contain a given commit.</p>
1051 </li>
1052 <li>
1053 <p>An array of <code>N</code> 8-byte unsigned values, each of which is
1054 interpreted as an offset (relative to the beginning of the
1055 <code>.bitmap</code> file) at which a pseudo-merge bitmap for this commit can
1056 be read. These values occur in no particular order.</p>
1057 </li>
1058 </ul>
1059 </div>
1060 </li>
1061 <li>
1062 <p>Positions for all pseudo-merges, each stored as an 8-byte unsigned
1063 value (in network byte-order) containing the offset (relative to the
1064 beginning of the <code>.bitmap</code> file) of each consecutive pseudo-merge.</p>
1065 </li>
1066 <li>
1067 <p>A 4-byte unsigned value (in network byte-order) equal to the number of
1068 pseudo-merges.</p>
1069 </li>
1070 <li>
1071 <p>A 4-byte unsigned value (in network byte-order) equal to the number of
1072 unique commits which appear in any pseudo-merge.</p>
1073 </li>
1074 <li>
1075 <p>An 8-byte unsigned value (in network byte-order) equal to the number
1076 of bytes between the start of the pseudo-merge section and the
1077 beginning of the lookup table.</p>
1078 </li>
1079 <li>
1080 <p>An 8-byte unsigned value (in network byte-order) equal to the number
1081 of bytes in the pseudo-merge section (including this field).</p>
1082 </li>
1083 </ul>
1084 </div>
1085 </div>
1086 </div>
1087 </div>
1088 </div>
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1090 <div id="footer-text">
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